Limits

Every limit the API enforces, in one place.

Files

What	Limit	Over-limit response
CSV recipients file	5 MB	413 File too large. Maximum 5MB.
Excel recipients file	10 MB	413 File too large. Maximum 10MB.
PDF background	20 MB	400 PDF must be under 20 MB
Logo image	5 MB	400 Logo file must be under 5 MB
Return-address logo	5 MB	400 Logo file must be under 5 MB
Each placed image	5 MB	400 Image file must be under 5 MB
Images per campaign	5	400 At most 5 images are allowed
Whole multipart campaign body	40 MB	413 Request body too large. Maximum 40MB.

Two different codes for "too big"

Per-part image and PDF limits report 400 validation_failed, while the recipients-file and whole-body limits report 413 payload_too_large. Handle both.

Accepted image types: PNG and JPEG only. Anything else is 400 Logo must be a PNG or JPG image / Image must be a PNG or JPG image.

Recipients

What	Limit
Inline recipients per campaign create	5,000 rows
Custom fields per recipient	16
Custom-field policies per request	16

Beyond 5,000 recipients, either import into a list first and send with listId, or split into several campaigns. There is no limit on how many recipients a list may hold.

Field lengths

Field	Max
Campaign name	200
List name	200
Recipient name	200
Recipient street	255
Recipient postCode	20
Recipient postTown	100
Recipient country	100
Custom-field key	64 (alphanumeric + underscore)
Custom-field value	512
returnAddress	1,000
QR description	500
search query	200
Idempotency-Key	255 (minimum 1)

Exceeding any of these is 400 validation_failed with the field named in details.fieldErrors.

Pagination

What	Value
Default limit	20
Maximum limit	100
Minimum limit	1

Requests

What	Limit
Rate, per key	100 requests / 60 s
Rate, per account (all keys together)	300 requests / 60 s, burst 60
Rate, per IP	A flood shield; not published
Key expiry	1–365 days, if set at creation

See Rate limits.

Retention

What	Behaviour
Inactive list	Deleted after 90 days without activity
Campaigns of a deleted list	Kept, with listId and listName set to null

Activity means adding a recipient, importing, or using the list in a campaign. Reading does not count. See Lists & recipients.

Uniqueness

Rule
One QR code per campaign — a second is 409 Campaign already has a QR code
One campaign per Idempotency-Key per account — a repeat replays the original
A QR slug is globally unique and permanent

PDF expectations that are not enforced

Your responsibility

The API validates only that a PDF part is declared application/pdf, is under 20 MB, and begins with a PDF signature. It does not check:

• page size (must be A4, 210 × 297 mm),
• page count (1, or 2 with hasBackPage),
• orientation,
• whether artwork avoids the reserved address zones.

A non-conforming PDF is accepted and printed as-is. See PDF campaigns.

No documented limit

These have no API-enforced ceiling, which is not a promise that they are unbounded:

• recipients per list,
• lists per account,
• campaigns per account,
• concurrent in-flight campaigns.

If you are planning a send far beyond your normal volume, confirm capacity before relying on it.