That is simply not true. For Client-Server communication there is IMAP (for management of your mailbox) and SMTP (for sending emails) which is also used for Ser

That is simply not true. For Client-Server communication there is IMAP (for management of your mailbox) and SMTP (for sending emails) which is also used for Server-Server communication. The fact that clients such as Thunderbird (or mutt) exist and work with basically all email hosts is a testament to this fact.