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.
Find the record
Open the matching contacts from the Bounced card in the campaign report. In the contact profile, open the Activity tab and click the campaign's row. The row shows Bounced with the reason, and the detail box shows the Bounce code. See Read a campaign report to find the report.
A Hard bounce indicates a permanent problem that requires the address to be excluded from future sends. These addresses are blocked.
A Soft bounce indicates a problem that may allow another send later, such as a full mailbox or a temporarily unreachable server. It does not guarantee that delivery will eventually succeed.
The sections below explain common bounce reasons and what you can do. Codes are examples, and provider replies can vary. Each record’s hard or soft classification appears in the contact profile.
Hard bounces
Incorrect or closed addresses are common causes in this group.
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.
Soft bounces
Full mailboxes and temporary connection problems are common causes in this group. Sending again may be possible once the problem is resolved.
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 mailbox remained full, so the email could not be delivered despite repeated attempts.
Example code: 554 4.4.7. Attempts have ended. Wait for the recipient to clear space before sending again.
Expired, server unreachable
The recipient’s server could not be reached after repeated attempts, so the email was not delivered.
Example code: 554 4.4.7. Check the address domain. If the problem continues, contact the recipient’s technical team.
Delivery expired
Delivery was retried for a period of time, but the recipient’s server did not accept the email. Attempts for this email have ended.
Example code: 554 4.4.7. 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 spelling of the domain in the address.
Other rejections and blocks
Content, security rules or previous blocks can also prevent sending. The record shows whether these events are classified as hard or soft bounces.
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.
Risky address, not sent
This email was not sent because the address looked invalid or risky in the automatic check before sending.
Example code: no code. MailGraf did not send to this address, so the email never reached the recipient's server. The check stops addresses that are likely to bounce and protects your sending reputation. Remove the address from your list. If you are sure it is correct, share it with support.
General failure
The recipient's server did not accept the email.
Example code: no code. The bounce did not match a known reason. If the same address bounces again, share it with support.
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.
What happens when delivery is delayed?
Delivery delayed means the email has not yet been delivered and will be retried. Delivery expired means those attempts have ended without delivering the email.
For example, a full mailbox may prevent delivery on the first attempt. If it remains full during later attempts, delivery expires. If the record says 14 hours, the email was retried over that period.
Each Delivery delayed event appears as its own row on the contact's Activity tab. 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 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 email could not be delivered after repeated attempts, and those attempts have ended. The bounce explanation in the contact profile gives the reason, such as a full mailbox or an unreachable server.
Are 552 5.2.2 and 554 4.4.7 the same?
No. 552 5.2.2 means the recipient’s mailbox has no space. 554 4.4.7 means delivery was retried but did not succeed. For example, the mailbox may have remained full throughout those attempts.
What does Risky address, not sent mean?
The address looked invalid or risky in the automatic check before sending, so the email was not sent. Remove the address from your list, or share it with support if you are sure it is correct.
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