Did anything change with your email configuration? Either on the server end or your settings in XF's control panel? Are there any server error logs in XF's control panel relating to mail not being sent?
The problem is.. Gmail only allows a set number of emails to be done a day. With 3500 emails to be sent, you are FAR exceeding what they allow.
Google Apps limits it to 2000 a day if I remember correctly, and a Google Apps email typically doesn't end in .gmail.
I think these are still Gmails limits Google Gmail Email Sending Limit
- 500 emails per day when sending from their web interface
- 100 emails per day when sending from a desktop email client
- 10mb per message
You are going to need to use your hosting providers email (and odds are they limit you to a set number per day also) or get on a VPS/dedi where you can utilize your own MTA for mail.
Another option, if wanting to stay on a shared hosting provider is to use something like Mandril for your email.
Did you review the log at /home/worldaidxm/www/internal_data/bdmails_1425225817_d18677ab48db69c927ff1f7e3ab5c788.log and see what it told you? It will usually give you an error. I have a feeling you either don't have Mandril set up correctly or your login you are using is invalid.
I'm assuming you have signed up with Mandrill, gotten the API key and put it in as you were supposed to, and reflected the correct domain? You also have to configure on the Mandril end also, and if I remember correct set up some DNS entries that Mandrill requires. It's pretty much explained by reading through the resource discussion for that add-on.