Why can’t I send email from my iPhone? It says I can’t connect to my aerver

Try first to optimize the range of the mobile network, see this Apple article:

If you see No Service or Searching on your iPhone or iPad

If you see No Service or Searching on your iPhone or iPad - Apple Support

Charge the battery > 70%.

Check the outgoing server & account settings, see -> IMAP account basic settings

https://support.microsoft.com/en-us/office/imap-account-basic-settings-0a3f843d-d858-4527-ba0c-b57aeb83bf4e

See also -> Change or update your email password

https://support.microsoft.com/en-us/office/change-or-update-your-email-password-58b62e89-6a9b-467b-8865-d5633fcacc3f