On 13 Sep 2016, at 14:10, JosC wrote:
In een bericht van 13-9-2016 15:55:
Usually the sender will disconnect when they see your SIZE banner,
so you never have an opportunity to send them anything. All you'll
see in your logs is a connect/disconnect.
With Thunderbird I sometimes do see a message that attachments are
oversized. Who is generating this message? Thought it might be
postfix?
By "message" do you mean an actual piece of email reporting the problem
or a notification in the Thunderbird user interface?
Email messages reporting a delivery failure are almost always generated
by some MTA, e.g. Postfix. There's a standard format for such failure
report messages that most MTAs use which includes an explicit
"Reporting-MTA" field identifying the generator of the report.
A "message" from the TBird UI (i.e. an alert window or error message in
a status area of the main widow, etc.) is almost certainly generated by
TBird itself. The first step in submitting a message is the MUA (TBird)
saying "EHLO <hostname>" to the MSA/MTA (Postfix) and getting a response
listing the supported extensions to SMTP supported by that server.
Example:
$ telnet localhost 587
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 toaster.scconsult.com ESMTP Postfix
EHLO localhost
250-toaster.scconsult.com
250-PIPELINING
250-SIZE 40960000
250-ETRN
250-STARTTLS
250-XCLIENT NAME ADDR PROTO HELO REVERSE_NAME PORT LOGIN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250 SMTPUTF8
quit
221 2.0.0 Bye
Connection closed by foreign host.
All of the lines starting with a 3-digit number are coming from Postfix.
The line "250-SIZE 40960000" tells the client that the server is willing
to consider accepting a 40MB message, because I have "message_size_limit
= 40960000" in my main.cf. A well-designed MUA will parse the EHLO
response for a "SIZE" line and if the declared size is smaller than the
message it wants to send, simply send a 'quit' and tell the user that
their message was too big. If a message is rejected later by a policy
server or milter that imposes more complex rules regarding message size,
the client should pass back to the user whatever rejection reply Postfix
passed along from that external program. For example, I use code run via
the MIMEDefang milter to impose smaller limits on some sender/recipient
combinations which can reply with text saying the message is too large.
In that case, Postfix is sending an explicit rejection response to the
client and it is up to the client to relay that back to the user.
