I have set up my personal environment SMTP server using an office365 account. This works well when I am sending emails from the address that has user access to the account. I would, however, need the ability to send emails from various email addresses as determined by the users of the various applications. In other words, the "From" field of the email will be different from the default sender email address.

I understand that sending emails from various accounts will have to be allowed by the SMTP server I am using. So I am asking if any one is aware of any good options for achieving this. 

The shared mailbox option for office365 is not an option because I would have to give mailbox permissions in advance. Since I will not always know the sender's email address in advance, this will not help me.