is verifiable using their message system or just to see if it's true.

Since PayPal doesn't have a message system, yet, anything important they send you can be verified by visiting their web site the normal way.

I get so many from both that, just for fun, I look at the properties of the message. Often I see the native language is Russian, or it's got multiple recipients, or they forget to forge the from as PayPal.com and have it some other off-the wall e-mail address. My favorites are the ones that are so sloppy as to use the priority e-mail symbol in the heading. Neither eBay or PayPal EVER do this. It's a dead giveaway without even reading the e-mail or looking at the headers.