Mail server error

Generally your email provider (gmail, hotmail, AOL, etc...) can be reached using their webmail site (support section) on a computer, or by phone.

Are you now saying that the "mail server error" is coming from an Apple email address (@icloud.com, @me.com e @mac.com)?

Should be this case, you can contact Apple Support directly, using this link:--> Contact Apple for support and service

Regards

Giulio

In such a situation, you should check your SMTP/IMAP/POP3 parameters with your email provider.

Regards

Giulio