Understand bounce codes
Read hard and soft bounces, codes such as 554 4.4.7 and delivery delays, then decide what to check next.
A bounce is recorded when the recipient’s server does not accept an email. Read the code, explanation and hard or soft classification together. Do not decide what happened from the first digit of a code alone.
Find the record
Open the matching contacts from the Bounced card in the campaign report. In the contact profile, inspect the bounce event and Server reply under View details. See Read a campaign report to find the report.
A Hard bounce identifies a problem that requires the address to be excluded from future sends. These addresses are blocked. A Soft bounce describes a potentially temporary problem, such as a full mailbox or an unreachable server. It does not promise that delivery will eventually succeed.
Find the reason and next step
The sentences below match the explanations in contact profiles. Codes are common examples, and provider replies can vary. Use the event classification and full server reply alongside them.
Mailbox does not exist
There is no mailbox at this address; it may be mistyped or closed.
Example code: 550 5.1.1, 5.1.10, 5.4.1 (Microsoft), 5.5.0. Check the address with its source. Do not resume sending to a closed mailbox.
Mailbox closed
This mailbox is closed or no longer in use.
Example code: 550 5.2.1. Ask the recipient for their current address through another channel.
Mailbox full
The recipient's mailbox is full; the server did not accept the email.
Example code: 552 5.2.2. Allow time for the recipient to clear space. Do not immediately resend the email.
Expired, mailbox full
The recipient's mailbox is full; delivery was retried for 14 hours and never accepted.
Example code: 554 4.4.7 with 4.2.2 inside. Retries have ended. Confirm the mailbox is available before a new send.
Expired, server unreachable
The recipient's server could not be reached for 14 hours, so delivery expired.
Example code: 554 4.4.7 with 4.4.x inside. Check the address domain. If the problem continues, contact the recipient’s technical team.
Delivery expired
The recipient's server did not accept the email for 14 hours, so delivery expired.
Example code: 554 4.4.7. Read the server reply in the details. Expiry alone does not prove the address is wrong.
Server unreachable
The recipient's server could not be reached or the address could not be routed.
Example code: 4.4.1, 5.4.4. Check the domain spelling and server reply.
Rejected by policy
The recipient's server rejected the email under a security or policy rule.
Example code: 550 5.7.1, 5.7.27. Check the sending domain and the rejection explanation. Share them with support if needed.
Content rejected
The recipient's server rejected the email content.
Example code: 5.7.1 (spam), 5.6.x. Review the email’s links, content and the reason given by the server.
Message too large
The email is larger than the recipient's server accepts.
Example code: 5.2.3, 5.3.4. Reduce the email size and share large files through links.
Suppressed by provider history
This address bounced before, so the email was not sent.
Example code: Provider suppression record. Review the previous block. Do not reimport the address to bypass it.
General failure
The recipient's server did not accept the email.
Example code: no code. Read the server reply in the details.
Other or undetermined
The recipient's server did not accept the email; no reason was given.
Example code: unclear. Do not infer a cause from this label alone. Share the campaign and event time with support.
Distinguish retries from delays
When 554 4.4.7 is accompanied by 840 minutes, delivery was retried for 14 hours before expiring. An inner 4.2.2 reply points to a full mailbox. An inner 4.4.x reply or a connection error points to an unreachable server. The same outer code can therefore have different explanations.
552 5.2.2 reports a full mailbox directly. These records describe different stages: one can explain the rejection, while the other confirms that retries have ended.
Consecutive Delivery delayed events for the same campaign on the same day can be grouped under a badge such as ×10 in the contact profile. Click the badge to see the times. Events on different days remain separate. A delay is not a final bounce, so look for the later delivery or bounce result.
Before the next send
Do not reimport blocked addresses to include them in a send. Check the source of your list and follow Verify and clean your email list. Verification checks the technical state of an address, not the recipient’s marketing consent.
For an unexplained error, or one affecting many contacts, share the campaign name, event time and server reply with support.
For account reviews, complaint thresholds and pre-send checks, see Understand sending and list rules.
Frequently asked questions
What does 554 4.4.7 mean?
The delivery retry window has expired. The inner server reply may explain that the mailbox was full or the server could not be reached.
Are 552 5.2.2 and 554 4.4.7 the same?
No. 552 5.2.2 reports a full mailbox. 554 4.4.7 reports an expired retry window, which may still have a full mailbox as its underlying cause.
Does Delivery delayed ×10 mean ten emails were sent?
No. Repeated delay events for the same campaign are grouped together. Open the badge to inspect their times.
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