@julesssbar: Is the issue affecting all contacts/email addresses, or just certain ones? Also, do the emails contain any large file attachments? If you sign in to your account via a browser app (Samsung Internet or Chrome) are you able to send emails as you would normally?
To troubleshoot the situation, please try heading to Settings > Apps > Samsung Email > Force stop > Storage > Clear cache > Restart your phone, then attempt to send another email.
