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4

For sendmail, I do two things: Make sure my /etc/hosts file follows the standard documented here. If I need to present a specific outgoing server name, I define confDOMAIN_NAME in sendmail.mc to reflect the right name: define(`confDOMAIN_NAME', `mail.juicybanana.com')dnl


4

One solution is increased monitoring e.g. raise alerts when the number of messages from individual ip-address/user account suddenly increases. That may be followed by rate limiting. The other is egress filtering on the SMTP servers you provide to your customers, similar to how you do spam filtering on incoming e-mail.


3

Your question says you are "struggling to work out why this waited for so long before being re-tried", but it seems to me that those logs are definitive: your mail server isn't waiting 12 days before re-trying sending. It's retrying it quite often (though without all the logs I can't say how often), but the remote server is being consistently unavailable. ...


2

Apparently I've been hoist by my own methodology's petard. It now looks like the reason that the date header caused the message to be accepted by the smart host without being delivered is that I didn't change the timestamp in the header with each test. So the smart host saw multiple message with identical message IDs and timestamps coming in, and just ...


2

You say the mail server is going to be sending to the internet. That means it's going to connect to public mail servers, and the first thing it will do (as part of the SMTP HELO) is declare its own FQDN. If you use a false or non-resolving FQDN here, a lot of mail servers are going to refuse to talk to you any further, or will use that as a strong ...


2

The recommended way is to fill the /etc/hosts with records, one for each ip address of the host, with a configured hostname of this host (with the appropriate command), so sendmail won't need to query the DNS. "He", whoever this is, is wrong. He is showing you a perfect way to shoot your own leg.


2

My guess, this header just some meta-information about DKIM processing milter, especially the deprecated dkim-milter. X-DKIM: Sendmail DKIM Filter v2.8.2 DOMAIN SOMEVALUE DOMAIN: Hostname in FQDN format SOMEVALUE: queue ID when this message processed by sendmail For example, X-DKIM header from this question. Received : from localhost ...


1

I found the problem by looking in the Apache logs. Apparently, the FTP password was hacked and there was a post.php file placed in all of the web directories that allowed them to send emails.


1

I had a similar issue recently with one of the domains we relay for. There was a single message in the queue for that domain which caused their gateway to hang and not accept the message. This arrived while their gateway was unavailable for maintenance (so we built up a queue of messages for them before they were back in service). On subsequent queue runs ...



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