i'm having this issue with 2 businesses i'm working on. we are sending out automated verification emails to users signing up for our saas. these emails can take up to 15 minutes to arrive in the Inbox - there appears to be no pattern.
we use Mandrill as one transaction provider and sendgrid as another. the emails are shown as sent/delivered but the emails are taking far longer to show in the Inbox.
Anyone having the same issue? Any ideas on fixes?
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.