Zoho 550 5.4.6 Unusual sending activity detected
550 5.4.6 Unusual sending activity detectedZoho unusual sending activity blockPermanent: retrying will not helpFrom Zoho Mail
550 5.4.6 Unusual sending activity detected
What it means
Zoho returns this to its own user when its outbound systems see sending that does not match the account’s normal pattern. Outgoing mail is paused while Zoho checks. Like 554 5.1.8, it is about your account, not the recipient.
The enhanced code 5.4.6 means “Routing loop detected” in RFC 3463. Zoho reuses it here for its activity block, so do not go looking for a loop in your DNS or forwarding.
Common triggers include a jump in recipients per day, logins from new locations, or many messages to new contacts. Once Zoho confirms the account is safe, sending is usually restored.
Likely causes
- A login from a new country or device followed by sending, which suggests a compromised account.
- A sudden bulk send far beyond the account’s normal volume.
- Many sends to new contacts with a high bounce rate.
- An app with stored credentials sending in a loop.
How to fix it
- Sign in to Zoho Mail and follow any prompt to verify the account.
- Change your password, enable two-factor authentication, and review recent logins and app passwords.
- Stop any app or script that sends through the account until you know it is not the cause.
- Contact Zoho support if sending is not restored after you have secured the account.
Checks that apply
- SPF Check Confirms your domain authorizes Zoho to send, ruling out authentication problems once sending resumes.
- DMARC Check Shows your DMARC policy, so spoofed mail claiming your domain gets rejected while you clean up.
FAQ
- Is there a routing loop?
- No. Zoho reuses the 5.4.6 code for its activity block; the RFC meaning does not apply here.
- Did someone hack my account?
- Maybe. Check recent logins and sent items. If you do not recognize the activity, change your password right away.