The Way that universal email works is to compile the email message, then pass it on top the SMTP server.
Once it is passed to the SMTP Server, it is up to the SMTP server to read the header, look at the to address and relay the email to that address.
Any delay on the email being delivered would either be the SMTP Server queue being backed up, or the route that the email takes to it's final destination, or it could be a combination of both.
just like when you ping a website, it goes through a few differant routers, emails will pass through different routers on the way as well.
Where the email is being sent sometimes or slowly, that doesn't point to a problem with Universal Email compiling the message and passing it on, it points to a problem on the smtp server, or the message is being delivered but trapped as spam