Translation of sender IP address

[Ivan Labáth]

On Wed, Feb 26, 2020 at 05:05:26PM +0100, tubi webmail wrote:
> So NO rules regarding masquerading seems to be in use.

I would suggest you check your iptables nat table
# iptables --list -vn -t nat
alternatively check the output of
# iptables-save

Also, these days you might be using nftables:

# nft list ruleset   # probably, I don't use nftables

Regards,
Ivan