Question How to allow a website to be accessed via IPv4 or IPv6 address but emails via mailer / Postfix / SMTP only via IPv4?

[MHC_1]

Server operating system version

Alma Linux 9.7

Plesk version and microupdate number

18.0.74

How to allow a website to be accessed via IPv4 or IPv6 address but emails via mailer / Postfix / SMTP only via IPv4?

I think the title pretty much covers it. We have various domains on a shared server with both an IPv4 and IPv6 server address but emails being sent from the IPv6 address are being persistently marked as spam . Both addresses emails work and are set up with all the usual anti spam stuff.

So, what we want to do is to have the website and other assets available on both IPv4 and IPv6 but the email comms of the account to only be accessible and send emails via IPv4 .

How can we do this on the Plesk GUI?

 

[Sebahat.hadzhi]

Hi, @MHC_1 . Could you please try setting Tools & Settings > Mail Server Settings > Outgoing mail mode to "Send from the specified IP addresses":

• https://support.plesk.com/hc/en-us/...s-in-Plesk-for-Linux-with-Postfix-mail-server

I hope that helps!

 

[MHC_1]

Hi, @MHC_1 . Could you please try setting Tools & Settings > Mail Server Settings > Outgoing mail mode to "Send from the specified IP addresses":

• https://support.plesk.com/hc/en-us/...s-in-Plesk-for-Linux-with-Postfix-mail-server

I hope that helps!

The problem with this is that it's a shared server and the other option on that listing of choices "Send from domain IP addresses and use domain names in SMTP greeting" is the much preferred option for deliverability . How do we send from the Specific IP address (IPv4) and retain using the domain name in the SMTP greeting?

 

[ChristophRo]

"Send from domain IP addresses and use domain names in SMTP greeting" is surely the worst option to choose from, if one is concerned about mails getting marked as spam or even rejected.

I would bet that 99.99% of the installations where that option is enabled, use non valid (i.e. RFC conformity) configurations...

 

[MHC_1]

@ChristophRo explain why

 

[ChristophRo]

for once, because you will (most likely) not be able to get the reverse DNS record(s) right. (see also https://support.plesk.com/hc/en-us/...rent-outgoing-mail-modes-work-on-Plesk-server)

this problem affects ipv4 as well as ipv6, but when it comes to emails and spam protection/detection, the use of ipv6 is always a bit problematic and often requires a more stringent configuration, because receiving mailservers can't rely on DNSBLs (with very few exceptions they only work for ipv4) and rate limits, in order to make a basic assertion on the authenticity and reliability of an email.

for example, while it's still possible today, to successfully send emails to Gmail/Office365 recipients without proper SPF or DKIM record on the sender domain, this only works for IPv4 connections.
When using IPv6, a valid SPF and/or DKIM configuration is a must requirement in order to be able to send an email to Gmail/Office365