diff --git a/AGENTS.md b/AGENTS.md
index 34678b3..1ebe11f 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -292,7 +292,10 @@ exactly 140.
   inside a `<base>-<n>` id.** An SMSC may answer `submit_sm_resp` in hex and write the receipt's
   `id:` in decimal, so one transform over both sides cannot make them equal — `smsIdFormat` names
   `receipt` and `submitResp` separately and reads both into a plain decimal value before `smsIds`
-  and `dlr.smsId` are compared. Omitting a place is what leaving it alone means, so there is no
+  and `dlr.smsId` are compared. `submitResp` covers the `receipted_message_id` TLV too, which SMPP
+  3.4 5.3.2.26 defines as the id the `submit_sm_resp` carried: naming one notation for whichever id
+  a receipt yields would break the peer that sends both, whose TLV correlated before the option was
+  set. Omitting a place is what leaving it alone means, so there is no
   `raw` notation, and a caller-supplied formatter is refused because it would make the promise that
   those two are comparable unverifiable — `onRequest` and the PDU on the `dlr` event are the escape
   hatches, and the `onReceipt` hook in todo.md is the seam if one is wanted. An id no notation reads
diff --git a/README.md b/README.md
index a35c594..ddb8833 100644
--- a/README.md
+++ b/README.md
@@ -172,6 +172,8 @@ before you see them:
 const { err, session } = await client({ smsIdFormat: { receipt: 'decimal', submitResp: 'hex' } });
 ```
 
+`receipt` is the notation of the receipt body's `id:` field, `submitResp` that of the `message_id`
+a `submit_sm_resp` carries — and of a receipt's `receipted_message_id` TLV, which is that same id.
 An id that is not a number in the notation given is left exactly as it arrived, and the PDUs carry
 what the peer wrote either way — `pduObjs` from the send, and the second argument of the `dlr` event.
 
diff --git a/src/client.ts b/src/client.ts
index ba07528..0176f19 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -168,7 +168,7 @@ async function connect(options: ClientOptions, log: SmppLog): Promise<Result<{ s
 	const checked = checkSessionOptions(options);
 
 	if (checked.err) {
-		log.warn('client - option out of range', { message: checked.err.message });
+		log.warn('client - unusable option', { message: checked.err.message });
 
 		return { err: checked.err };
 	}
diff --git a/src/dlr.ts b/src/dlr.ts
index c736ff9..adb2829 100644
--- a/src/dlr.ts
+++ b/src/dlr.ts
@@ -1,7 +1,7 @@
 import type { MessageState } from './defs/constants.ts';
 import type { ParamValue } from './defs/types.ts';
 import type { PduObject } from './pdu.ts';
-import type { SmsIdNotation } from './sms-id.ts';
+import type { SmsIdFormat } from './sms-id.ts';
 import { consts, constsById, messageTypeOf } from './defs/constants.ts';
 import { decodeMessage } from './message.ts';
 import { normaliseSmsId } from './sms-id.ts';
@@ -164,11 +164,16 @@ function receiptBody(pduObj: PduObject): string {
 function receiptId(
 	tlvId: ParamValue | undefined,
 	receipt: Receipt | undefined,
-	notation: SmsIdNotation | undefined,
+	format: SmsIdFormat,
 ): string | undefined {
-	const id = nonEmptyText(tlvId) ?? nonEmptyText(receipt?.id);
+	// SMPP 3.4 5.3.2.26: the TLV is the id the submit_sm_resp carried, where the body's is a rendering.
+	const fromTlv = nonEmptyText(tlvId);
 
-	return id === undefined ? undefined : normaliseSmsId(id, notation);
+	if (fromTlv !== undefined) return normaliseSmsId(fromTlv, format.submitResp);
+
+	const fromBody = nonEmptyText(receipt?.id);
+
+	return fromBody === undefined ? undefined : normaliseSmsId(fromBody, format.receipt);
 }
 
 function isMessageState(name: string | undefined): name is MessageState {
@@ -192,14 +197,14 @@ function receiptStatus(
 }
 
 /** The delivery report a deliver_sm carries, or nothing when it carries a message instead. */
-export function dlrFromPdu(pduObj: PduObject, notation?: SmsIdNotation): Dlr | undefined {
+export function dlrFromPdu(pduObj: PduObject, format: SmsIdFormat = {}): Dlr | undefined {
 	const type = messageType(pduObj);
 
 	if (type === 'other') return undefined;
 
 	const body = receiptBody(pduObj);
 	const receipt = body === '' ? undefined : parseReceipt(body);
-	const smsId = receiptId(pduObj.tlvs.receipted_message_id?.tagValue, receipt, notation);
+	const smsId = receiptId(pduObj.tlvs.receipted_message_id?.tagValue, receipt, format);
 	const { statusId, statusMsg } = receiptStatus(pduObj.tlvs.message_state?.tagValue, receipt);
 
 	if (type === 'unmarked' && (smsId === undefined || statusMsg === undefined)) return undefined;
diff --git a/src/incoming-requests.ts b/src/incoming-requests.ts
index b0d93be..7b4f038 100644
--- a/src/incoming-requests.ts
+++ b/src/incoming-requests.ts
@@ -3,7 +3,7 @@ import type { OnRequest } from './session-options.ts';
 import type { PduObject } from './pdu.ts';
 import type { Session } from './session.ts';
 import type { SmppLog } from './log.ts';
-import type { SmsIdNotation } from './sms-id.ts';
+import type { SmsIdFormat } from './sms-id.ts';
 import { Reassembler, decodeSegments } from './reassembly.ts';
 import { bindCommands, defaults } from './session-options.ts';
 import { concatInfo } from './udh.ts';
@@ -19,7 +19,7 @@ export type IncomingRequestsOptions = {
 	maxReassembly?: number | undefined;
 	onRequest?: OnRequest | undefined;
 	reassemblyTimeout?: number | undefined;
-	receiptIdNotation?: SmsIdNotation | undefined;
+	smsIdFormat?: SmsIdFormat | undefined;
 	session: Session;
 	systemId?: string | undefined;
 };
@@ -30,8 +30,8 @@ export class IncomingRequests {
 	private readonly log: SmppLog;
 	private readonly onRequest: OnRequest | undefined;
 	private readonly reassembler: Reassembler;
-	private readonly receiptIdNotation: SmsIdNotation | undefined;
 	private readonly session: Session;
+	private readonly smsIdFormat: SmsIdFormat;
 	private readonly systemId: string;
 
 	constructor(options: IncomingRequestsOptions) {
@@ -44,8 +44,8 @@ export class IncomingRequests {
 			maxOctets: options.maxOctets,
 			timeout: options.reassemblyTimeout ?? defaults.reassemblyTimeout,
 		});
-		this.receiptIdNotation = options.receiptIdNotation;
 		this.session = options.session;
+		this.smsIdFormat = options.smsIdFormat ?? {};
 		this.systemId = options.systemId ?? defaults.systemId;
 	}
 
@@ -101,7 +101,7 @@ export class IncomingRequests {
 
 	/** SMPP carries a mobile-originated message and a delivery receipt on the same command. */
 	private async onDeliverSm(pduObj: PduObject): Promise<void> {
-		const dlr = dlrFromPdu(pduObj, this.receiptIdNotation);
+		const dlr = dlrFromPdu(pduObj, this.smsIdFormat);
 
 		if (!dlr) {
 			this.onMessage(pduObj);
diff --git a/src/session-options.ts b/src/session-options.ts
index 3370fef..9905f14 100644
--- a/src/session-options.ts
+++ b/src/session-options.ts
@@ -145,17 +145,17 @@ function checkSmsIdFormat(smsIdFormat: unknown): VoidResult {
 		return { err: new Error('smsIdFormat names a notation per place, as { receipt, submitResp }') };
 	}
 
-	const allowed = smsIdNotations.join(' or ');
-
-	for (const place of smsIdPlaces) {
-		const notation = smsIdFormat[place];
+	for (const [place, notation] of Object.entries(smsIdFormat)) {
+		if (!smsIdPlaces.includes(place)) {
+			return { err: new Error(`smsIdFormat has no ${place}, name ${smsIdPlaces.join(' or ')}`) };
+		}
 
 		if (notation === undefined || isSmsIdNotation(notation)) continue;
 
 		// String() throws on a null-prototype object, and this value is whatever the caller passed.
 		const got = typeof notation === 'string' ? notation : typeof notation;
 
-		return { err: new Error(`smsIdFormat.${place} must be ${allowed}, got ${got}`) };
+		return { err: new Error(`smsIdFormat.${place} must be ${smsIdNotations.join(' or ')}, got ${got}`) };
 	}
 
 	return {};
diff --git a/src/session.ts b/src/session.ts
index 95ca5f8..e18fd53 100644
--- a/src/session.ts
+++ b/src/session.ts
@@ -120,8 +120,8 @@ export class Session extends EventEmitter<SessionEvents> {
 			maxReassembly: options.maxReassembly,
 			onRequest: options.onRequest,
 			reassemblyTimeout: options.reassemblyTimeout,
-			receiptIdNotation: options.smsIdFormat?.receipt,
 			session: this,
+			smsIdFormat: options.smsIdFormat,
 			systemId: options.systemId,
 		});
 		this.pending = new PendingRequests(this.log);
diff --git a/src/sms-id.ts b/src/sms-id.ts
index 6f54ef6..202161a 100644
--- a/src/sms-id.ts
+++ b/src/sms-id.ts
@@ -3,18 +3,17 @@ const notations = {
 	hex: { digits: /^[0-9a-f]+$/i, prefix: '0x' },
 };
 
+const places = ['receipt', 'submitResp'] as const;
+
 /** The notation a peer writes message ids in. */
 export type SmsIdNotation = keyof typeof notations;
 
 /** The notation per place the peer writes an id. An omitted place is left as it arrived. */
-export type SmsIdFormat = {
-	receipt?: SmsIdNotation | undefined;
-	submitResp?: SmsIdNotation | undefined;
-};
+export type SmsIdFormat = Partial<Record<typeof places[number], SmsIdNotation | undefined>>;
 
 export const smsIdNotations: string[] = Object.keys(notations);
 
-export const smsIdPlaces: (keyof SmsIdFormat)[] = ['receipt', 'submitResp'];
+export const smsIdPlaces: readonly string[] = places;
 
 export function isSmsIdNotation(value: unknown): value is SmsIdNotation {
 	return typeof value === 'string' && Object.hasOwn(notations, value);
@@ -25,11 +24,10 @@ const maxIdLength = 64;
 
 /**
  * The id as a plain decimal value, so an SMSC that answers a submit in one notation and writes the
- * receipt in another still correlates. An id the notation cannot read is left as it arrived, which
- * is what leaves a `<base>-<n>` id whole for DlrMerger.
+ * receipt in another still correlates.
  */
 export function normaliseSmsId(id: string, notation: SmsIdNotation | undefined): string {
-	if (notation === undefined || id.length > maxIdLength) return id;
+	if (!isSmsIdNotation(notation) || id.length > maxIdLength) return id;
 
 	const { digits, prefix } = notations[notation];
 
diff --git a/test/dlr.test.ts b/test/dlr.test.ts
index b569394..2dc499c 100644
--- a/test/dlr.test.ts
+++ b/test/dlr.test.ts
@@ -208,28 +208,35 @@ describe('dlrFromPdu()', () => {
 	});
 
 	test('reads the id in the notation the peer writes receipts in', () => {
-		const hex = dlrFromPdu(deliverSm('id:1a2B stat:DELIVRD err:000 text:'), 'hex');
+		const hex = dlrFromPdu(deliverSm('id:1a2B stat:DELIVRD err:000 text:'), { receipt: 'hex' });
 
 		assert.ok(hex);
 		assert.equal(hex.smsId, '6699');
 		assert.equal(hex.receipt?.id, '1a2B', 'the receipt itself keeps the id as it arrived');
 
-		assert.equal(dlrFromPdu(deliverSm('id:0000123 stat:DELIVRD'), 'decimal')?.smsId, '123');
-		assert.equal(dlrFromPdu(deliverSm('nothing scrapable here', {
+		assert.equal(dlrFromPdu(deliverSm('id:0000123 stat:DELIVRD'), { receipt: 'decimal' })?.smsId, '123');
+	});
+
+	// SMPP 3.4 5.3.2.26 makes the TLV the id the submit_sm_resp carried, not the body's rendering.
+	test('reads the receipted_message_id TLV in the notation the peer answers a submit in', () => {
+		const marked = deliverSm('nothing scrapable here', {
 			receipted_message_id: { tagValue: 'FF' },
-		}, 0), 'hex')?.smsId, '255');
+		}, 0);
+
+		assert.equal(dlrFromPdu(marked, { submitResp: 'hex' })?.smsId, '255');
+		assert.equal(dlrFromPdu(marked, { receipt: 'hex' })?.smsId, 'FF');
 	});
 
 	test('leaves an id the notation cannot read as it arrived', () => {
-		assert.equal(dlrFromPdu(deliverSm('id:beef-1 stat:DELIVRD'), 'hex')?.smsId, 'beef-1');
-		assert.equal(dlrFromPdu(deliverSm('id:1a2b stat:DELIVRD'), 'decimal')?.smsId, '1a2b');
+		assert.equal(dlrFromPdu(deliverSm('id:beef-1 stat:DELIVRD'), { receipt: 'hex' })?.smsId, 'beef-1');
+		assert.equal(dlrFromPdu(deliverSm('id:1a2b stat:DELIVRD'), { receipt: 'decimal' })?.smsId, '1a2b');
 		assert.equal(dlrFromPdu(deliverSm('id:0195f0c7 stat:DELIVRD'))?.smsId, '0195f0c7');
 	});
 
 	// Number() reads 9007199254740993 as ...92, which correlates a receipt to the wrong send.
 	test('reads an id past the safe integer range without losing a digit', () => {
 		assert.equal(
-			dlrFromPdu(deliverSm('id:9007199254740993 stat:DELIVRD'), 'decimal')?.smsId,
+			dlrFromPdu(deliverSm('id:9007199254740993 stat:DELIVRD'), { receipt: 'decimal' })?.smsId,
 			'9007199254740993',
 		);
 	});
diff --git a/test/session-extras.test.ts b/test/session-extras.test.ts
index 3adf63b..81c564a 100644
--- a/test/session-extras.test.ts
+++ b/test/session-extras.test.ts
@@ -79,7 +79,7 @@ function peerOf(smpp: SmppServer): Session {
 	return peer;
 }
 
-async function sendReceipt(peer: Session, smsId: string): Promise<void> {
+async function sendReceipt(peer: Session, smsId: string, tlvSmsId = smsId): Promise<void> {
 	const sent = await peer.send({
 		cmdName: 'deliver_sm',
 		params: {
@@ -90,7 +90,7 @@ async function sendReceipt(peer: Session, smsId: string): Promise<void> {
 		},
 		tlvs: {
 			message_state: { tagValue: consts.MESSAGE_STATE.DELIVERED },
-			receipted_message_id: { tagValue: smsId },
+			receipted_message_id: { tagValue: tlvSmsId },
 		},
 	});
 
@@ -831,15 +831,21 @@ describe('message id notation', () => {
 
 		assert.ok(session);
 
-		const reported = once<Dlr>(resolve => { session.on('dlr', resolve); });
+		const reported = once<[Dlr, PduObject]>(resolve => {
+			session.on('dlr', (dlr, pduObj) => { resolve([dlr, pduObj]); });
+		});
 		const sent = await sendOne(session, 'one segment');
 
 		assert.deepEqual(sent.smsIds, ['6699']);
 		assert.equal(paramText(sent.pduObjs[0]?.params.message_id), '1a2b', 'the PDU keeps the id it carried');
 
-		await sendReceipt(peerOf(smpp), '6699');
+		// The receipt renders the id in decimal and mirrors the answered one in its TLV, as the spec has it.
+		await sendReceipt(peerOf(smpp), '6699', '1a2b');
 
-		assert.equal((await reported).smsId, sent.smsIds[0]);
+		const [dlr, pduObj] = await reported;
+
+		assert.equal(dlr.smsId, sent.smsIds[0]);
+		assert.equal(paramText(pduObj.tlvs.receipted_message_id?.tagValue), '1a2b');
 	});
 
 	test('leaves the segment ids of a multipart send to merge as they are', async t => {
@@ -874,6 +880,11 @@ describe('message id notation', () => {
 		assert.match(checked.err.message, /smsIdFormat\.receipt/);
 		// The shape todo.md sketched, which a caller without types would otherwise pass unnoticed.
 		assert.ok(checkSessionOptions({ smsIdFormat: 'hex' }).err instanceof Error);
+		assert.match(
+			checkSessionOptions({ smsIdFormat: { receipts: 'decimal' } }).err?.message ?? '',
+			/receipts/,
+			'a misspelled place is the same silent no-op',
+		);
 		assert.equal(checkSessionOptions({ smsIdFormat: { submitResp: 'hex' } }).err, undefined);
 	});
 });
diff --git a/todo.md b/todo.md
index a082f0a..4a3b0db 100644
--- a/todo.md
+++ b/todo.md
@@ -156,6 +156,11 @@ session message is a change to every call site.
 - [ ] **Coverage reporting.** `node --test --experimental-test-coverage` works today; nothing
       publishes the numbers.
 
+- [ ] **A receipt whose fields are separated by anything but a space reads as one field.**
+      `parseReceipt()` takes `id:` as everything up to the next space, so a peer writing CRLF
+      between fields yields an id of `1a2b\r\nstat:DELIVRD` — one nothing correlates and no
+      notation can read. Every field pattern has the same shape. Raised by review, 2026-08-30.
+
 - [ ] **An `onReceipt` hook.** Receipt text is only loosely specified and operators disagree on it,
       but `dlrFromPdu()` is wired into `IncomingRequests` with no seam of its own: an application
       facing a format we do not parse has to take the whole PDU on `onRequest` and reimplement the