[Question] Email flow when using with milter

Mark Sapiro mark at msapiro.net
Tue Jun 26 14:43:51 UTC 2018

On 6/26/18 12:24 AM, Eoin Kim wrote:
> Thanks Mark,
> So, if I interpret your comment in my own way, if the milter rejects the message, no one (both sender and receiver) will know about what happened to the message. Am I following you? If so, that wouldn't be a pleasant situation for me.

The sending MTA will receive an SMTP 5xx status with a reason provided
by the milter. What happens then depends on how the mail was sent, but
the original sender should be notified somehow. The difference is any
delivery status notification which may be backscatter to a spoofed
sender will come from the sending MTA or upstream and not from your
server. This is a good thing.

> Are there any features similar to milters I can use in MailScanner? I believe, SPF, DKIM, RBL check is possible with it, correct? Thanks again.

The one big downside of MailScanner is your server has already accepted
the mail before MailScanner sees it. Thus, any backscatter generated by
a MailScanner notice comes from you. MailScanner can check RBLs.
Generally SPF and DKIM validation are done by the incoming MTA which
generates results headers that are checked by SpamAssassin running by

MailScanner does support custom functions as a hook to your own code,
but this is somewhat limited and doesn't support a 'milter' interface.

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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