Hello, I've been busy on these days trying to solve a problem with Postfix that drove me nuts.
Sporadically (let's say one in hundred e-mails) my Postfix had problems for delivering messages with ~3 MiB of attachment to some e-mail hosts. DSN service returned the final notice of delivery to the user and logs displayed an error like "timed out while sending message body". These hosts were not of those "difficult" ones like Hotmail, Gmail, Yahoo! or the like that because to their high volume of traffic implement additional (and sometimes strambotic) measures to prevent spam and such "anti-all" systems that may require a different transport definiton in Postfix to get e-mails delivered. Moreover, these hosts were not e-mail servers that are behind Cisco PIX devices or using MS Exchange servers that are also well-known to be conflictive to "dialogue" with. Nope, I was having problems for delivering to common, small hosts of mid- size companies, one of the hosts running a Debian system, like mine. So I had to run some tests to find out what could be the problem here. I first tried to define a less conservative values (by increasing the time) for "smtp_data_done_timeout", "smtp_data_xfer_timeout" and "smtp_data_init_timeout" but this had no effect at all and again, some e- mails were still undelivered. Googling around I found some posts and articles¹ pointing to the MTU value (my bonded interface was set by default to 1500) and as I had nothing to lose, I changed this and lowered to 1400. This turned out to work wonders and since then (that's more than a week ago) I still had no other DSN delivery errors. Besides, e-mails in deferred queue that could not be sent in that time, after lowering the MTU value were also delivered with no apparent problems. I'm still monitoring this but if this is the "cure" to prevent such errors, are there any expected drawbacks for lowering MTU "system-wide"? The server has dual gigabit NIC which are bonded (in backup mode) and server itself is behind a FTTH gigabit router. The server also hosts a web server. Any comments or experiences on this are welcome :-) ¹http://www.hsc.fr/ressources/cours/postfix/doc/faq.html#timeouts Greetings, -- Camaleón -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/pan.2011.08.31.16.09...@gmail.com
