In Office 365, this permission allows users other than the mailbox owner to use the mailbox to send messages. After this permission is assigned to a delegate, any message that a delegate sends from this mailbox will appear as if it was sent by the mailbox owner. However, this permission doesn't allow a delegate to sign in to the user's mailbox.
Send On Behalf Of
In Office 365, this permission allows a delegate to use this mailbox to send messages. However, after this permission is assigned to a delegate, the From address in any message sent by the delegate indicates that the message was sent by the delegate on behalf of the mailbox owner.
Office 365 service accounts are intended to be used for shared/changing roles (e.g., info, secretary, webmaster, newsletter, feedback, etc.) or service/programmatic access (e.g., printers, copiers, mailers). Service accounts can be accessed via all Outlook clients. Learn more about the types of accounts available within Office 365.
A sub-domain is a domain that is part of a larger domain; the only domain that is not also a sub-domain is the root domain. For example, doit.wisc.edu and engr.wisc.edu are sub-domains of the wisc.edu domain.