Email courier is an individual who gets out of their chair and approaches someone's desk or workstation in a work environment almost immediately after sending them an email, usually to make sure that the email has been received and that they can get a reply right away.
Email courier指在办公室里刚给别人发完邮件就立马起身来到收件人的工作台旁边，跟人家确认邮件是否收到，还希望人家立即给回复的人，即“电邮快递员”。
For example:
Bill: I just sent you an email. Did you get it?
Bill: 我刚给你发了封邮件，你收到了吗?
Mike: Probably, I haven't checked.
Mike: 可能收到了吧，我没查邮箱。
Bill: Can you check?
Bill: 你能查一下吗?
Mike: Uh yeah, looks like I got it.
Mike: 呃，对，收到了。
Bill: Thoughts?
Bill: 你什么想法?
Mike: My immediate thoughts are you're an email courier and a douchebag.
Mike: 我现在的想法是，你是个电邮快递员，而且是个讨厌鬼。