Add maximum length condition for e-mail address

[danielstgt]

According to the RFC, an e-mail address can have a maximum of 254 characters.

Since addresses that do not fit in those fields are not normally useful, the upper limit on address lengths should normally be considered to be 254.

Source: RFC Errata Report

Further information:
Stackoverflow: What is the maximum length of a valid email address?

Instead of referring to the max condition manually, the global maximum length makes sure that all e-mail addresses are conform to the RFC specification.

This pull request adds this condition.

Off-topic: Other positive side effects are, that some database fields with a 255 VARCHAR limit, which is quite common for an e-mail address, won't be exceeded.

[coveralls]

Coverage remained the same at 88.235% when pulling 4630246 on danielstgt:patch-1 into c26eb70 on yiminghe:master.