I can't really speak toward whether mailing eggs decreases viability or not. I can say that the eggs I've hatched came through the mail. An additional risk of getting them that way is that the postal service may x-ray the package. The first shipment I got was clearly marked on all sides with bright, colorful stickers - 'live embryos, do not x-ray!' and 'hatching eggs, handle with care!'. That was the first time I've ever tried to hatch eggs of any kind, and out of 18 Serama eggs, I got 4 healthy, thriving chicks that are currently 3 weeks old. There were 8 eggs that showed no signs of fertility, 3 that started to develop and then stopped, and 2 that went full term but appear to have died right before internal pipping. I currently have 22 more Serama eggs that I got through the mail in the incubator, set this morning, from a different source. The package arrived with 'Eggs' written in black sharpie on the top, nothing else. No request not to x-ray, no colorful stickers to draw attention to the fact that it's a fragile package that needs gentle handling. I just wait and see whether any of them end up being viable. Whether the losses in the first batch were due to shipping or my own inexperience, I cannot tell you.
