451 4.7.0 Recipient rejected (R21): error No outbound mail

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Joined: Mon Jan 23, 2017 5:19 pm

451 4.7.0 Recipient rejected (R21): error No outbound mail

Postby rcouch » Mon Jan 23, 2017 5:40 pm

MailEnable server Standard Edition. Inbound mail works fine. All outbound mail results in a delivery subsystem error stating:

Message is waiting at Bains.Local for delivery to na0100.smtpout.com.

Message delivery has been delayed to the following recipients:
Recipient: [SMTP:elockhart@netrocketpc.com]
Reason: Remote SMTP Server Returned: 451 4.7.0 Recipient rejected (R21): 1484856468.73503.cal1-mh746 []

Server has been running fine for years until last week when an employee clicked on a link in an email which I suspect was a trojan. Thoroughly cleaned all PCs with MalwareBytes and SuperAntiSpyware. Some items detected and cleaned. Checked blacklists and found them listed on six lists. Got them cleared from these lists but same problem persists. Checked activity and debug logs but they just seem to confirm the information shown above. Any ideas?

Site Admin
Posts: 8599
Joined: Mon Mar 22, 2004 4:44 am
Location: Melbourne, Victoria, Australia

Re: 451 4.7.0 Recipient rejected (R21): error No outbound mail

Postby MailEnable-Ian » Mon Jan 30, 2017 11:40 pm


Looks like the remote mail server is still rejecting your inbound message because the IP has been detected on a blacklist. Or the sender address has been blacklisted by the recipient. Not much MailEnable can do to help here.

Ian Margarone
MailEnable Support

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