I have found with working with a Canon 580EXII and a 430EX that you require line of sight between the flashes to fire correctly when the 580EXII is the master. A way around this is to get a 3rd party wireless flash controller or in the newer canon DSLRs have wireless control from the on body flash which can get around some minor corners as the flash lights up the area and hit the IR receiver on the flash. the on camera flash will flash before the shutter opens so it doesnt effect the photo.

How to troubleshoot Canon Speedlites that are not firing at the same time?
By "by ok to use" I mean:


are MTA agents receiving emails from my server going to reject my
email
if not, are they going to make other kind of bad treatment for my
emails (marking as spam, unsafe and so...)?


...or is it just better idea to stick with non-encrypted emails?
