Limits

“Per day” is a UTC calendar day (resets at 00:00 UTC), “per month” a UTC calendar month, “per hour” a UTC clock hour. A “network” is one IPv4 address or one IPv6 /64.

Per account

Limit	Sandbox	Claimed (not available yet)	When reached
Live inboxes	1	3	409 inbox_limit
Inbox creations per day, the signup inbox included	3	10	429 inbox_create_limit, Retry-After until 00:00 UTC
Messages received per month, all inboxes together	1,000	5,000	Further mail is rejected (mailbox unavailable)
Size of one received message	10 MiB	10 MiB	The mail is rejected (mailbox unavailable)
Long-polls held at once (wait and events?wait= together)	5	5	429 too_many_waits, Retry-After: 1
Sandbox period	7 days	—	The account works as expired. See Accounts

Rejected mail is not counted as received, and the agent is not told about it. GET /v1/account shows usage.received_this_month.

Signup

Limit	Value	When reached
Signups per network per day	20	429 signup_limit, Retry-After until 00:00 UTC
Burst guard, per network, on the challenge and on signup separately	about 20 requests per minute (approximate)	429 rate_limited, Retry-After: 60
Challenge lifetime	10 minutes	400 pow_expired
Uses per challenge	1	400 pow_reused
Proof-of-work difficulty	20 leading zero bits by default	400 pow_invalid

Requests

Limit	Value	When reached
JSON body	16,384 bytes	413 payload_too_large
agent_name, name, display_name	64 characters	400 invalid_request
Idempotency-Key	1–255 printable ASCII characters, kept 24 hours	400 invalid_request
wait hold (timeout)	0–60 seconds, default 25	400 invalid_request
wait results (limit)	1–50, default 10	400 invalid_request
wait lookback (since default)	10 minutes	—
Message list page (limit)	1–100, default 20	400 invalid_request
Events per call (limit), events hold (wait)	1–100 (default 100); 0–60 seconds (default 0)	400 invalid_request
from, subject filters	200 characters	400 invalid_request
Messages scanned per filtered call	the 500 newest	A filtered list page can be short while has_more is true
Thread view	the newest 500 messages	truncated: true
Original message with include=raw	2 MiB	raw: null with raw_error

Stored message fields

Field	Cap
text	256 KiB
reply_text	64 KiB
subject	2 KiB
to	100 addresses
Attachments	50 per message
snippet	200 characters

A cut field gets the signal content_truncated (attachments_truncated for attachments). The original message stays stored.

Extraction

Limit	Value
Text scanned	the subject and the first 100,000 characters of text
Other plausible codes (otp_candidates)	4
Links returned	20 (of the first 200 examined)

Unusual volume of verification mail

When an account receives more than 20 verification-code mails from at least 5 sender domains within an hour, otp_flagged_until (in GET /v1/account) is set for 24 hours. Mail is never rejected or delayed because of it. While it is set, an account that is not claimed (today: every account) may run at most 10 extractions per UTC hour (POST …/extract and wait?extract= together):

• POST /v1/messages/{id}/extract answers 429 extract_limit, with Retry-After until the next UTC hour;
• wait?extract= returns the remaining messages with extracted: null and extract_limited: true.

Reading messages is never capped.

Headers

Retry-After (whole seconds) comes with rate_limited (60), signup_limit and inbox_create_limit (until 00:00 UTC), too_many_waits (1), extract_limit (until the next UTC hour), signups_disabled (3600) and, only after repeated insert races, address_unavailable on POST /v1/inboxes (1). There are no X-RateLimit-* headers.

Not available yet

• A request-rate limit per API key is planned.
• Sending limits do not exist, because there is no sending.