You may choose to have multiple email addresses associated with a single mailbox. The 'standard' way of getting that done is simply by adding those aliases to your mailbox - however, the problem with that approach is that you cannot send as those email addresses. There are a couple of workarounds. One is to create 'dummy' POP3 accounts associated with those aliases in Outlook. The down-side of that approach is that, well, you need to create dummy POP3 accounts for each user, which involves some level of management overhead. The alternative way, described in this article, is to create a distribution list for your alias, then give yourself Send As rights to that distribution list. The down side of this approach is that your Address Book will now contain extra entries.
Prerequisite: connect to your Exchange Online account via PowerShell. Use this PowerShell profile script to automate the process!
In this scenario, i want to be able to receive mail sent to firstname.lastname@example.org, and send as that email address as well.
1. Create a new distribution group:
new-distributiongroup -name email@example.com -displayname "Sales" -alias ilya.lehrman.sales -members firstname.lastname@example.org -primarysmtpaddress email@example.com
2. Remove restriction to receive only from internal to organization senders:
set-distributiongroup firstname.lastname@example.org -hiddenfromaddresslistsenabled $false -requiresenderauthenticationenabled $false
3. The final step is to grant myself SendAs rights:
add-recipientpermission email@example.com -accessrights SendAs -trustee firstname.lastname@example.org -confirm:$false
You have to wait until your changes take effect, and after they do, I will be able to send as email@example.com, and will receive all email sent to firstname.lastname@example.org. Note that you should not hide the distribution group from the Global Address List, because if you do, you will no longer be able to use the send-as functionality.