I just made a clean install of the XenForo forums on my server. Upon completion the first thing I did was to create a test user account. After a few minutes I noticed I did not receive the confirmation e-mail to activate the account and realized I made a typo when entering the e-mail address. I selected my account's Contact Details, corrected my e-mail address, entered my password as required, then saved the changes.
After I saw the "Your account is currently awaiting confirmation. Confirmation was sent to xxx" screen, I pressed the Resend Confirmation Email link. A moment later I realized it still showed the old (incorrect) e-mail address. I pressed refresh (F5) and then the correct e-mail address appeared so once again I pressed the Resend Confirmation Email link. After waiting 5 minutes, no email came. I re-checked the email address in my Contact Details and am 100% sure it is correct. I tried Resend Confirmation Email again, but it had no effect.
I sent a test mail to my account and it was received instantly. I tried setting up another forum account and I received the Confirmation Email within seconds. After ?20+ minutes I still have not received the email for the original account.