On Thu 01/Sep/2022 18:33:48 +0200 Hendrik Boom wrote:
> On Thu, Sep 01, 2022 at 11:30:43AM +1000, onefang wrote:
>>
>> The problem with PTRs is that I run several domains from the one IP
>> address, and PTR can only point to one of those. It costs money to get
>> more IPs, my pension is barely coping with the recent cost of living
>> increases.


That is what MX records are for. It's straightforward to set up
mail.example.com with its PTR having a single name that matches. Then, for all
the other domains set the MX to it. For example:

whatever.domain IN MX 2 mail.example.com.


the HELO (or EHLO) command also uses mail.example.com. Nobody will notice any
difference unless the analyze the message header.

From: uses the virtual domain <user@???>.
DKIM signatures with d=whatever.domain.
SPF records at whatever.domain have the address of mail.example.com.
DMARC record for whatever.domain has rua=reports@???.


> If IP's are expensive, would it help to switch to IPv6?


Not all MXes have IPv6 address. You need an IPv4 to send to an IPv4-only MX.

Google is said to be more severe with mail coming from IPv6 addresses.


HTH
Ale
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