Hi Hasham! I think the use of webmail.domain.com versus mail.domain.com likely originates in old email server types/providers that defaulted to these hostnames when deploying a new domain. So, this probably comes down to preference. If you have clients migrating from servers where the webmail.domain.com hostname was used previously though I recommend keeping an A or CNAME record in DNS for it to make sure user's old bookmarks still work. I hope that helps!