An instance manager created a mailing list named avivey with your email address:

mysql> select * from user where id = 2\G
*************************** 1. row ***************************
                        id: 2
                      phid: PHID-USER-37mrt3obcxjlad35pv72
                  userName: avivey
                  realName: avivey
               dateCreated: 1533253856
              dateModified: 1533330289
...
             isMailingList: 1                                <<<--- Note Flag Set
...
1 row in set (0.00 sec)

To do this, they needed to go through this workflow and ignore the colored box telling them not to keep going:

Realistically, many users do, in fact, go through this workflow and ignore the box, and "destroy a mailing list someone created" is probably on the top 10 list of support issues we deal with by frequency. See T13156 for details and plans to improve this.

Here, you probably do want to Create New Account, then choose some other email address like avivey+sure+wish+my+address+wasnt+stolen+already@gmail.com or whatever. This will give you a fully functional instance account with an unusual address, but you can't have your normal address because a mailing list already has it.

I think this is all about as reasonable as we can get it, and T13156 is the best pathway forward: rewrite the user creation flow to make this mistake extremely difficult even if you don't read big colorful warning boxes.

(Just merge this into T13156 if that makes sense?)