Email Receipt Delayed

When testing my Universal Emails, receipt is often delayed 30-45 minutes. At first I thought I had made a mistake and they were no longer working. However, eventually they show up. I'm only sending 2 emails at a time so I doubt Yahoo thinks it needs to slow me down. I searched the forum but could find no other cause for delayed receipt. Any ideas? Since they eventually show up this is not fatal but it slows down testing and may concern website users if their expected emails take 30 minutes to show up. Thanks.

Emails can sometimes take a while to be relayed. In many cases, an email will travel through a number of different servers to reach the recipient. The more servers the message is relayed through the longer it will take.

I used www.mxtoolbox.com to analyse my email headers once the emails finally arrived. It confirms that Yahoo is holding them for 20 mins+ for some reason which Yahoo cannot explain. Sometimes they are not delayed. Sometimes they are. They pick on UE emails the most but also delay others. Hopefully when my testing settles down, Yahoo will stop flagging these emails.

thanks for the link to that tool, that looks handy.