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MailMarshal Temporarily Rejecting Email

MailMarshal Temporarily Rejecting Email – When sending email to a MailMarshal server, the server responds with a the following error:

‘421 SMTP service is temporarily unavailable’

This is a temporary rejection of email by the MailMarshal server and email will start to queue up for recipient on the sending mail server.

This is a result of DOS (Denial of Service) and DHA (Directory Harvest Attack) attack prevention settings on the MailMarshal server. If a lot of email is being sent to the recipient from a single IP address, the MailMarshal server believes this to be a potential attack and will temporarily reject the email.

To prevent this, the recipient will have to whitelist the IP addresses of the sending mail servers in their MailMarshal server.

in Email Security

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