[Mimedefang] Milter: data, reject=451 4.7.1 Please try again later

[Paul Murphy]

Rick asked:

> Is
>   define(`SMTP_MAILER_MAX',15000000)
> as recommended below the same as
>   define(`confMAX_MESSAGE_SIZE', '15000000')dnl
> 
> or is there a subtle difference between them. We have the 
> latter defined in our .mc file to protect against excessively 
> sized messages, but are we still vulnerable to running out of 
> memory and/or swap space.

The confMAX_MESSAGE_SIZE applies to all messages, whereas the first version
only applies to the SMTP mailer (SMTP/ESMTP).

In configurations where local messages can be larger, as for example where
the mail host also provides POP3 or IMAP4 services to users, you may want to
have a different limit for external mail - delivery to a local POP3 mailbox
uses the LOCAL mailer, and would not be affected by the SMTP limit.

Just in passing, if you are using ESMTP and the sender supports it as well,
the size limit is checked at the "MAIL FROM" stage, where ESMTP adds the
"SIZE=xxxx" parameter.  Without ESMTP, the message is received in full, then
the size is checked against the limit.  For this reason, some sites force all
mail to come in through an ISP's mail server which is known to speak ESMTP on
the final hop, so that denial of service is much more difficult.

Best Wishes,

Paul.