Half of the questions tagged with email-client are also tagged with email (62 / 130) .
Questions about email clients, mail transfer agents and email software configuration. Questions about webmail are off-topic.
I don't think we need both email and email-client, since they're basically the same. Both of them refer to email clients and not webmail, which is off-topic.
If email refers only to the mails themselves and not email clients such as Gmail, Outlook and Thunderbird then we have a lot of retagging to do.
I suggest removing email-client (making it a synonym of email) and using emailname-of-the-email-client instead (e.g emailgmail for Gmail emails related questions).