New members not receiving passwords

I’ve tried various SMTP plugins, yet this issue has not been resolved. New members only receive passwords when they use the “Forgot Password” feature, but this is not a long term solution! Also, whenever I send a test email to myself via the SMTP plugin, it goes through immediately. And yes, I made sure to set up a domain-based “from” address, and basically did everything that was recommended to me by various people, support, and developers. What could be going wrong here??

Thanks in advance. Any advice would be more than welcome!