Not performing the same on all domains?

If your ESP's statistics tool gives you (as it should be) a view of the statistics broken down by the most represented domains in your broadcast, then you might from time to time see quite huge discrepancies between domains.

Why would that be?
Well there's several reasons that could be possible here...

1 - You went strait to the junk folder.
If SMTP logs indicate SPAM refused emails (SPAM bounce), there is no message sent back to indicate the fact your messages were delivered to the junk folder.
A very low open rate/click rate compared to other domains could then be explained by a junk filtered email, this is often true if you have a lower complaint rate than usual on these domains (people usually don't complain when a mail is ALREADY in the junk folder.

2 - Bounce messages issue.
Sometimes (but it's somewhat very rare) domains don't send back delivery error messages (bounce messages) to the broadcaster. This can either be due to a hardcore blacklisting or to a temporary issue.
In this case, your open/click rate will be calculated on the total volume of sent emails although some of the message were not delivered.

3 - Images blocking.
Some ESPs correct the number of openings automatically to take this issue into account, some others (like Cabestan for example) just keep the exact number of openings. As you probably know, openings are counted each time images (including the tracking pixel) are displayed.
Therefor, domains blocking images potentially have a lower number of openers. This discrepancy should be lower on the click rate in this case.

4 - Junk email addresses.
Today, people have several email addresses (a personal one and a professional one at least). Some people also have "junk" email addresses that they only read once in a while. Usually these email addresses are created either on disposable email domains or on freemail domains.
This can be spotted quite easily when you have systematically low open rates on the same domain.