Data point: Yesterday I received my account approval letter for my application through the AA emailed mailer. It confirmed the 50k/$2500 bonus.
And, today, I got another emailed mailer with the same offer. The last two came on the 11th of each month (1/11 and 2/11); this one came 3/6. My co-worker who also plays this game got one today as well.
It's looking like these emailed mailers might be a good replacement for the physical ones. They seem to come quite often, and don't have a long wait between opening the account and getting the first mailer (mine started coming the first month I had my account)