Issue SMTP error while using NAT address

[trumbaut]

I recently started using a floating IP address for my droplet at Digital Ocean, following the instructions at Default Plesk page is shown for a domain assigned on a floating IP address from DigitalOcean. However, after changing subscriptions to the new floating IP (which works fine for the assigned websites), sending mails for these domains fail. For example:

1A8D8401DC 1414 Thu Feb 15 21:12:11 SRS0=s2Gv=FJ=server.domain.tld=watchdog@domain.tld
(delivery temporarily suspended: connect to alt2.gmail-smtp-in.l.google.com[64.233.187.26]:25: Connection timed out)
address@gmail.com

I checked Plesk Help Center which did not help. Within /etc/postfix/master.cf, the right NAT address was set (although I wonder if the floating/public IP address should be mentioned here):

plesk-10.XXX.YYY.ZZZ- unix - n n - - smtp -o smtp_bind_address=10.XXX.YYY.ZZZ -o smtp_bind_address6= -o smtp_address_preference=ipv4

On the "Server-Wide Mail Settings" page, the "Outgoing mail mode" was set to "Send from domain IP addresses". After changing this setting to "Send from the specified IP addresses: <old static IP address>" mails were able to be sent again. However, I would like a solution where Postfix uses my floating IP address as external adresses instead of the old static IP address.

Is this a bug? Or can it be fixed in an other way?

Technical details:

• Plesk version: Plesk Onyx v17.5.3_build1705170317.16 os_CentOS 7
• OS: CentOS Linux 7.4.1708 (Core
• MTA: Postfix 2.10.1-6.el7

 

[MarkM]

The outgoing IP for Postfix will be the same IP that it's listening on.

You could set a default IP for all outgoing connections if you want;

When mail is sent from my server, QMail uses an incorrect IP for the connection. How do I change the IP used for outgoing connections from my server?

(Ignore the Qmail part, the resolution shows how to set a default IP for outgoing connections by creating a route)

 

[trumbaut]

Are you sure this will work for a NAT address? Which "src" address should be mentioned in that case: the internal address (10.XXX.YYY.ZZZ) or the public one (EEE.FFFF.GGG.HHH)?

At this moment, an "ip route" command only has details about the primary IP address (AAA.BBB.CCC.DDD) which I want to avoid using, and the internal address (10.XXX.YYY.ZZZ):

default via AAA.BBB.CCC.1 dev eth0
10.XXX.YYY.0/16 dev eth0 proto kernel scope link src 10.XXX.YYY.ZZZ
AAA.BBB.CCC.0/24 dev eth0 proto kernel scope link src AAA.BBB.CCC.DDD
169.254.0.0/16 dev eth0 scope link metric 1002

 

[MarkM]

Yep, your default route is going to be the public address you don't want to use. Edit the "src" on this entry and insert your floating IP.