[Fetchmail-users] Local delivery - smtp or sendmail

[Hans C. <fo...@gm...>]

I'm in the process of upgrading my ancient local-only little home mail 
server and was wondering how much it matters if I use smtp or sendmail for 
local delivery.

My system is Fedora 43:
   fetchmail: 6.5.6
   postfix:   3.10.3
   alpine:    2.26

Keep reading for details of my setup and why I'm asking.

My setup is only used for 2 users, with a few email addresses for each 
user.  The MTA is postfix, configured to listen only on loopback port 25 
with a self signed cert.  There is no access to this server from the 
outside.  The only things that access the MTA are on the same host: alpine 
for relaying outbound mail and fetchmail for inbound mail.

fetchmail is started/stopped daily for each user via cron and each user 
has the same basic fetchmailrc:

   set daemon 900
   set logfile log/fetchmail.log
   defaults
   timeout 120
   fetchall
   nokeep
   fetchlimit 50
   ssl

   poll ...
   poll ...
   poll ...

I'm trying to configure smtpd_sender_restrictions in postfix, mainly so 
I'll get an immediate failure if I've added a new email address that 
hasn't been configured in postfix.

The problem is, if I add smtp_sender_restrictions in the postfix config 
(main.cf), then those restrictions apply to all connections; both from 
alpine and fetchmail.  I'm fairly certain there's a way to distinguish 
this by adding something to master.cf (still figuring that part out), but 
the key is, there needs to be a way to distinguish between the two.  I 
think if fetchmail uses sendmail instead of smtp, I can use that to setup 
restrictions based on smtp connections (alpine/outbound) and restrictions 
based on sendmail connections (fetchmail/inbound).

Soooo, back to the original question... on my little local-only server are 
there any pros/cons I should be aware of if I add a fetchmail mda config 
line to use sendmail (or whatever the postfix equiv is) instead of the 
default smtp?

An alternative, might be to distinguish the two by the fact that alpine 
connects to smtp via ipv4 and fetchmail connects via ipv6.  Maybe I could 
use that - although I was considering completely disabling ipv6 since I 
don't plan to ever use it... at least not locally.  Then again, maybe this 
IS a use for ipv6.

Thanks for any advice.