is csf.allow mandatory ?

[FrenchFox]

When my csf.allow file is empty, I can't send (SMTP) or read (POP) emails on my server, it ends up with a timeout. Adding my IP in csf.allow, everything is ok.
I would like to be able to access my emails from anywhere, how should I do ? I have looked for a parameter in csf.conf for that, but have not found so far . Any help appreciated.

[Sergio]

Have you checked that your IP is not in a black list?
Check it at the following sites:
https://mxtoolbox.com/blacklists.aspx
https://talosintelligence.com/reputation_center
https://www.abuseipdb.com/

Sergio