+1

This would be a highly valuable feature for us as well.

This would be nice because my org uses aliased email addresses for some users and it would be helpful to assign multiple emails to the same user.

Reinforcing some of the comments here, this addresses issues for very common cases when merges and acquisitions happen.

We also have AD on-premises synchronized with Azure AD to provision accounts to JSM and part of those accounts don't have usernames that match with their email addresses (specially for third-party users).

This is a must have for us and we find awkward not to have a feature allowing to add another email address to accounts.

It's a big vote from me too.

We use Jira in our company, and we use Active Directory (on-prem synced to Entra).

Usually, our users have usernames/UPNs that do not correspond with their email addresses, so for us, there is a need to have mail aliases for login (SSO).

Also, some external users do not have a mailbox at all, so we need to have the ability to add an additional email account for the notifications to be sent.

With merger & acquisitions and spinoffs commonplace, there are often scenarios where users will have multiple email addresses and need to log on the different systems with different emails. This is sometimes true for extended periods of time after such corporate events occur. The lack of the ability to associate multiple emails with a single account creates enormous operational inefficiencies for companies that go through such events.

Similar to others, having the ability to force a user with multiple email addresses to log in using the correct address would help reduce headaches and steps for providing support.

Some employees are assigned multiple addresses to start based on the organization they're working in. Many employees have first.last@company and first.m.last@company. And every employee as a alphanumeric ID that drives our SSO, which differ from their name. It'd be very helpful if we could define say, four different email addresses that would all log in to the exact account we want them to log into.

My company continues to suffer in the exact same way as 820ef1cfdf61 mentioned.

My company just turned on ITSM, and this is a big issue when getting replies into tickets via email.  Having multiple domains associated with a single user would solve all of the issues.  

Working with a client going through a merger and thus having a set of users with one set of Active Directory / Email accounts migrating to a different set; in the interim, they're still using both accounts which means that again they might, say, open a Service Desk ticket from their new email but their account is associated with their old email.

Or if they've migrated to their new account for most purposes including JIRA, perhaps someone will CC them on a Service Desk ticket using their old email address (because it's what they're used to).

For this client, the pain will slowly go away, because they will presumably move towards using the new account for everything and deprecate/remove the old account, but for now it's going to add to the friction.