Thunderbird on Linux forwarding to alias on localhost ignores nsswitch.conf settings
Thunderbird 115.13.0 (64-bit) on Linux using filters to forward to an alias on localhost ignores the nsswitch.conf settings and attempts to send the email to the main configured SMTP server instead of via the localhost SMTP server for the email address being forwarded to, which is process@localhost.
This process alias is defined in the /etc/aliases file and my nsswitch.conf file has file dns as the hosts: values.
The alias being sent to is supposed to process the email being forwarded and write the result to a file.
Opaite Mbohovái (1)
Thunderbird has no idea about your conf file. It uses DNS. Whatever the operating system resolves the address in settings to, that is where Thunderbird will attempt to send the mail
The SMTP used to send mail can be a somewhat complex issue, made more so by selecting messages to forward from filters. Not withstanding that it should be the SMTP specified in the identities settings and failing that the one specified in the outgoing server (SMTP) as default.