Webapp verification emails are becoming snail emails

Email is one of those technologies which makes no real assurance about delivery speed. Which is to say that the receiving party can delay it substantially as a spam-fighting technique (e.g. Gmail) and you cannot REALLY complain because email makes no assurance.

If you want near instant delivery then may I suggest Text Messages? They will often be delivered within a minute and cost very little with the right provider (e.g. Twilio).

For Mandrill, did you set up DKIM on it? I am running verification e-mails via Mandrill and right now they are getting sent more or less real time.

Do you really need to have eMail verification before the user is allowed to do anything?

In my application I let the user use the service for a week before actually doing any kind of blocking, simply displaying a bright red banner at the top of the page will prompt the majority of people to login to their eMail and verify, and for the ones that are waiting for an email it's no bit issue.

May be also think about sending an email and have a button/link for people that are still waiting, then use something like Twilio to verify them via SMS or Call if it really is vital to prove their identity before any kind of access is given.

Don't require verification for the first hour if you can, and try not to worry about it, or change your provider.

In the end, you only have control over how fast your mail is sent. The e-mail provider of the client determines when it is received.

Good on you for tracking and measuring it though.

Those delays can be caused by greylisting.

http://en.wikipedia.org/wiki/Greylisting