SMTP error 553: What it means and how to fix it
SMTP error 553 overview:
- SMTP error 553 is a permanent rejection (5xx). The message won’t be delivered until the issue is resolved.
- It is usually caused by one of four issues. Formatting, filtering, blocklisting, or relay restrictions.
- Use the bounce text to narrow it down. The message usually points to what you need to fix.
SMTP error 553 means the receiving server rejected the message because of a mailbox issue, a relay restriction, or a spam rule.
Sendmarc helps you keep SPF, DKIM, and DMARC aligned across your domains, strengthening authentication and supporting sender reputation – so fewer legitimate emails get blocked by spam filters.
What SMTP error 553 means
An SMTP 553 error means “Requested action not taken: mailbox name not allowed.” The receiving server rejected the email because something about the address or sender was unacceptable.
Because this is a permanent failure (5xx), you’ll need to fix the underlying issue before delivery can succeed.
Common causes of SMTP error 553
- Invalid address format: The email doesn’t meet RFC formatting rules
- Spam filtering: The message was rejected due to a spam rule
- Blocklisting: Your sending IP has been blocklisted
- Relay denied: The server won’t relay email to that destination
Provider-specific 553 errors
Google (Gmail, Google Workspace)
| Error message | Meaning |
|---|---|
| 553 5.1.2 – The recipient address is not a valid RFC-5321 address | The address format isn’t RFC-5321 compliant |
Yahoo (Yahoo, AOL, Verizon)
| Error message | Meaning |
|---|---|
| 553 5.7.1 – Connections will not be accepted from x.xx.xx.xx | The sending IP is on a blocklist |
Email Security.cloud
| Error message | Meaning |
|---|---|
| 553 – Message filtered | The message was rejected due to spam filtering |
| 553 – you are trying to use me as a relay, but I have not been configured to let you do this | The server isn’t configured to relay email |
Zoho
| Error message | Meaning |
|---|---|
| 553 – Relaying disallowed | The server won’t relay email to that destination |
How to fix SMTP error 553
For address format issues
Step 1: Verify the email address format
Valid format requirements:
- No spaces in the address
- Valid characters only
- Proper domain with TLD
Step 2: Reference RFC 5321 standards
Valid examples:
- user@example.com
- name@example.com
- user+tag@example.com
Invalid examples:
- user @example.com (space before @)
- user@example (no TLD)
- user@@example.com (double @)
For spam filter triggers
If the error mentions filtering:
Step 1: Review your email content
- Check the subject line for spam trigger words
- Review links in the message
- Examine attachments
Step 2: Confirm authentication
Check that SPF, DKIM, and DMARC are passing for the sending domain.
Step 3: Contact the recipient’s admin
Ask about their content policies; they may be able to allowlist your domain.
For IP blocklist issues
Many email providers check your domain/IP against blocklists. If you’re seeing blocklist-related 553 errors:
Step 1: Check your blocklist status
Use Sendmarc’s blocklist checker to see which list you’re on, so you can follow the right delisting process.
Step 2: Request removal
- Fix the underlying issue first
- Submit a removal request
- Wait for processing
Step 3: Prevent future listings
- Authenticate all email (SPF, DKIM, DMARC)
- Monitor your sending reputation
- Keep clean mailing lists
For relay issues
If the error mentions relay configuration, contact the recipient and share the bounce message so their team can investigate.
Email authentication to prevent 553 errors
Proper authentication reduces the risk of blocklisting and spam filtering.
SPF
SPF tells receiving servers which sources are allowed to send on behalf of your domain.
Example SPF record:
| Host | Type | Value |
|---|---|---|
@ | TXT | v=spf1 ip4:192.168.0.1 include:mail.example.com -all |
DKIM
DKIM adds a cryptographic signature to your emails, so receiving servers can verify the message hasn’t been altered in transit.
Example DKIM record:
| Host | Type | Value |
|---|---|---|
selector._domainkey.yourdomain.com | TXT | v=DKIM1; k=rsa; p=[public key] |
DMARC
DMARC tells receiving servers what to do when authentication fails and provides reporting.
Example DMARC record:
| Host | Type | Value |
|---|---|---|
_dmarc.yourdomain.com | TXT | v=DMARC1; p=reject; rua=mailto:dmarc-reports@yourdomain.com; fo=1; |
Protect your sending reputation with Sendmarc
SMTP 553 errors can indicate that receiving servers don’t fully trust the sender. While some 553 bounces are address or relay related, others are tied to sending reputation, and improving authentication can help reduce avoidable blocks.
Sendmarc helps you:
- Standardize SPF, DKIM, and DMARC across domains, departments, and regions to reduce fraud risk.
- Monitor for spoofing, impersonation, and unauthorized sending to protect your brand.
- Keep authentication consistent across sending tools to improve the delivery of critical communications.
- Detect issues faster and reduce IT effort with hands-on support when problems arise.
Sendmarc gives you the visibility and control to keep authentication aligned, so you can reduce reputation-related filtering and avoidable blocks.
SMTP error 553 FAQs
Is a 553 error permanent or temporary?
A 553 error is a permanent rejection (5xx). A 553 rejection won’t resolve on its own unless something changes.
How do I know if my 553 error is a blocklist issue?
A 553 error is likely related to blocklisting when the bounce message names a list. In that case, use a blocklist checker to see whether your sending IP or domain is listed.
Can I fix relay-related 553 errors?
Not from the sender side. Relay-related 553 errors mean the server handling the delivery won’t relay mail to that destination (often shown as “relaying disallowed”). The recipient’s administrator needs to fix the relay configuration.