This answer will change as my research and testing continues.
As of August 12, 2017, I am accepting this as my answer, but I am going to continue to expand on this list as I find new potential alternatives. I still prefer Avast due to its memory footprint and cost effectiveness, but YMMV.
Just to make a note, I did some research based on the amavisd-...
Setting up a mail server once - and then never touch it again. Do you mean that? Please don't act like this! Administrating a mail server is more than setting it up, you should know the protocols, especially SMTP, you should know how how TLS works, how to prevent spammers and hackers from entering and abusing your system, how to detect attacks, how to detect ...
I don't think you understand how some of the packages you investigated work...
postfix is pure SMTP. When it receives messages, it passes off to a mail delivery agent like dovecot. A MDA is pure IMAP/POP3, not SMTP.
You can use postfix and dovecot together in many different configurations for having virtual users (no linux account needed), storing ...
Here is another alternative - Zoho Mail.
It can do catch all and forwarding.
All the pricing plans are lower than your current subscription of 6,5EUR.
(Note: They also have a free plan, but it does not support forwarding.)
There are domain registrar that provide the email catch all and forwarding service that is included in the domain registration fee or as an add on fee.
I assume you are now paying domain name registration fee (yearly) + GSuite fee (monthly). So it might lower your cost if you transfer your domain to such registrar. (Assuming you can/want to do that.)
If you ...
I'm not sure if a web service is an option for you, but we use FreshDesk - there is also a free plan.
Important features for us are:
Tickets can be created by mail, api call or by an embed form
You see if somebody is viewing or replying to the ticket
Merging of similar tickets
Assign tickets to people / groups
Welcome aboard. Your question is off-topic here, and will probably be closed or deleted, which is a pity because it is a good question – just asked in the wrong place. Please click the question mark at the top right of any of our sites to see what is on-topic for that site.
Firstly, do you actually want an answer to your question as asked?
1 Do you want ...