My landlord recently changed to a different ISP that blocks all outgoing requests on port 25, except towards their own SMTP-server. After getting my hands dirty by plowing throgh the sendmail documentation, located here, I figured out that it wasn’t very difficult to configure sendmail to relay all outgoing e-mails towards this server, thus solving the entire problem.
If you want all outgoing mail to go to a central relay site, define SMART_HOST.
I started by checking the sendmail configuration file, /etc/mail/sendmail.cf, that strictly specified “DO NOT EDIT THIS FILE! Only edit the source .mc file.“. Following this advice, I had to figure out where this .mc file was located.
I did a quick search for all files containing sendmail and cf on my local system, and discovered “/usr/share/sendmail/cf/cf/sendmail-slackware.mc“. That was indeed the correct file, and I simply added “define(`SMART_HOST’, `smtp.online.no’)“. To see the entire configuration file, expand the spoiler below.
| Spoiler Inside: modified sendmail-slackware.mc |
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dnl# This is the default sendmail .mc file for Slackware. To generate
dnl# the sendmail.cf file from this (perhaps after making some changes),
dnl# use the m4 files in /usr/share/sendmail/cf like this:
dnl#
dnl# cp sendmail-slackware.mc /usr/share/sendmail/cf/config.mc
dnl# cd /usr/share/sendmail/cf
dnl# sh Build config.cf
dnl#
dnl# You may then install the resulting .cf file:
dnl# cp config.cf /etc/mail/sendmail.cf
dnl#
include(`../m4/cf.m4')
VERSIONID(`modified Slackware Linux setup by VHA')dnl
OSTYPE(`linux')dnl
dnl# These settings help protect against people verifying email addresses
dnl# at your site in order to send you email that you probably don't want:
define(`confPRIVACY_FLAGS', `authwarnings,novrfy,noexpn,restrictqrun')dnl
dnl# No timeout for ident:
define(`confTO_IDENT', `0')dnl
dnl# Enable smtp.online.no as smarthost
define(`SMART_HOST', `smtp.online.no')dnl
dnl# Enable the line below to use smrsh to restrict what sendmail can run:
dnl FEATURE(`smrsh',`/usr/sbin/smrsh')dnl
dnl# See the README in /usr/share/sendmail/cf for a ton of information on
dnl# how these options work:
FEATURE(`use_cw_file')dnl
FEATURE(`use_ct_file')dnl
FEATURE(`mailertable',`hash -o /etc/mail/mailertable.db')dnl
FEATURE(`virtusertable',`hash -o /etc/mail/virtusertable.db')dnl
FEATURE(`access_db', `hash -T /etc/mail/access')dnl
FEATURE(`blacklist_recipients')dnl
FEATURE(`local_procmail',`',`procmail -t -Y -a $h -d $u')dnl
FEATURE(`always_add_domain')dnl
FEATURE(`redirect')dnl
dnl# Turn this feature on if you don't always have DNS, or enjoy junk mail:
FEATURE(`accept_unresolvable_domains')dnl
EXPOSED_USER(`root')dnl
dnl# Also accept mail for localhost.localdomain:
LOCAL_DOMAIN(`localhost.localdomain')dnl
MAILER(local)dnl
MAILER(smtp)dnl
MAILER(procmail)dnl
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Once that was done, I had to compile the configuration file with “m4 /usr/share/sendmail/cf/cf/my-sendmail.slackware.mc > /etc/mail/sendmail.cf“, and restart inetd and sendmail by running /etc/rc.d/rc.inetd restart && /etc/rc.d/rc.sendmail restart.
Problem solved, and I’m receiving my emails again!
