Membership confirmation

I'm having a problem with membership follow through.

Lot's of new members but some never follow, or confirm their accounts.

What's your best way for getting members to finalize the join process.

Please don't refer a module.

I know this might sound silly, but have you checked to make sure the emails aren't landing into a black hole of some kind?

Nathan might be correct.  I have several ISPs that have blocked emails from my server to their users based on a range of IPs; I think this is BS as they need to just block from the single IP address of spammers; not everyone in the range.  I got one ISP to accept my emails after filling out their form; I still have others to attend to.

The worst is Verizon. Which kind of makes sense if you think about it.

Verizon?  Oh yeah, the company that is pissing mad because they ruled that ISPs have to treat all traffic the same.  Companies getting to call their networks 4G and now 5G when they are only marginally better than they use to be; only in the good ol' US of A.

Not sure about where they land. How would I determine that?

The site mail is done with Mandrill because of blocking by some; I check all undelivered mail and remove those memberships.