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2

One solution is increased monitoring e.g. raise alerts when the number of messages from individual ip-address/user account suddenly increases. That may be followed by rate limiting. The other is egress filtering on the SMTP servers you provide to your customers, similar to how you do spam filtering on incoming e-mail.


2

Apparently I've been hoist by my own methodology's petard. It now looks like the reason that the date header caused the message to be accepted by the smart host without being delivered is that I didn't change the timestamp in the header with each test. So the smart host saw multiple message with identical message IDs and timestamps coming in, and just ...


4

For sendmail, I do two things: Make sure my /etc/hosts file follows the standard documented here. If I need to present a specific outgoing server name, I define confDOMAIN_NAME in sendmail.mc to reflect the right name: define(`confDOMAIN_NAME', `mail.juicybanana.com')dnl


2

You say the mail server is going to be sending to the internet. That means it's going to connect to public mail servers, and the first thing it will do (as part of the SMTP HELO) is declare its own FQDN. If you use a false or non-resolving FQDN here, a lot of mail servers are going to refuse to talk to you any further, or will use that as a strong ...


2

The recommended way is to fill the /etc/hosts with records, one for each ip address of the host, with a configured hostname of this host (with the appropriate command), so sendmail won't need to query the DNS. "He", whoever this is, is wrong. He is showing you a perfect way to shoot your own leg.


2

You probably don't have sendmail installed but have postfix instead. You can verify this by running rpm -qfi /usr/sbin/sendmail. As c4f4t0r commented, postfix is the default mailer in CentOS 6. Sendmail is available but not installed by default.


5

Some background Postfix inherited some features from older sendmail like milter and aliases. The file /etc/aliases is part of aliases inheritance and implemented by alias_maps. On the other side, postfix has virtual_maps/virtual_alias_maps for handle email aliasing. So what's the difference between them? Parameter alias_maps Used only for local(8) ...


1

/etc/aliases is there primarily for local delivery, for example, mail to root from cron, etc, it's nice to keep your local aliases separate, virtual_alias_maps can also be used with SQL DBs, and so on. virtual_alias_maps is for when you have virtual users (and virtual domains), often that do not map to system users, but if you don't have virtual domains, ...


0

I'm running a Postfix server and I encountered the same problem today. There are two issues to be aware of if you try to forward email from your server to a gmail account: First, Google will reject some spammy messages at the SMTP connection time. If that happens, then your MTA might actually send a bounce message back to the (alleged) sender; this is ...


0

Try checking that the linode host sees the right MX records for your destination domain... dig MX good domain.org That should show Google's servers. If not you've got a lower level problem. The domain part of sending address is typically derived from what is in /etc/hosts for the local machine. At the very least you want this to be the fqdn. You can ...


0

Figured this one out; just getting exim to use the Google Apps MX with a switch in hubbed_hosts.


0

The last part of that log excerpt confirms that the message was accepted by the recipient mail server at gmail: relay=aspmx.l.google.com. [[redacted]], dsn=2.0.0, stat=Sent (OK 1415320818 q110si8698921qgd.122 - gsmtp) The portion in parenthesis is part of the confirmation that the remote server gave back so if you had a support contact at google, they ...


2

As far as I know the support for subject alternative names is primarily a client side issue. There the SAN entries have to be checked when the request hostname doesn't match the Common Name in the certificate. Sendmail simply loads and presents the certificate and doesn't even need to interpret the SAN entries encoded in there, I think. But even if some ...


0

The answer was not to do what was in the comments, but rather the following. Hetzner servers attempt first to send mail over IPv6 if possible, so I needed to: add an AAAA forward record edit Hetzner robot to add a reverse IPv6 record. Also make sure your hostname matches the domain you want. So: edit /etc/hostname and /etc/hosts invoke-rc.d hostname.sh ...


1

It dynamically links to the version of openssl you have installed # ldd `which sendmail` | grep ssl libssl.so.10 => /usr/lib64/libssl.so.10 (0x00007f1ffec11000) libssl3.so => /usr/lib64/libssl3.so (0x00007f1ffdab5000) If you were to say install a source version over the rpm version and it didn't install those two libraries sendmail would not work ...


1

clientmqueue is for messages submitted by non-root users running sendmail locally on the host to deliver mail, and mqueue is for messages being processed by the running sendmail daemon (usually delivered by SMTP).



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