Issue of invalid email address for recommendation

[BorneoHunterGatherer]

Does anyone confront the same issue as mine? I am unable to save all of my recommenders in the section of recommendations successfully due to the issue of invalid email address. I am so sure of those email address I entered are correct and valid to use. This happened for application system of Virginia, UC Santa Cruz, Duke, and Georgia as well. 

[TakeruK]

Sometimes schools require recommenders to use their work email address and reject gmail, hotmail, yahoo, etc. email addresses. Maybe that is the problem?

[BorneoHunterGatherer]

6 minutes ago, TakeruK said:

Sometimes schools require recommenders to use their work email address and reject gmail, hotmail, yahoo, etc. email addresses. Maybe that is the problem?

Dear Takeruk, those email address I entered are all institutional working purpose one. I wonder that is anyone who applies for the same school list as mine confronted the similar issue here?