Companies offering free email generally expect to gain something in return. Some sell advertising banners that may slow down the connection to your email. Some services require a personal profile when you register and make money selling that information. Free email providers may disappear, so if it is important that the service remains available, choose a well-established provider. These services are sometimes abused by spammers, which may cause additional problems.
Some mailing lists restrict access from certain free services because of such problems.
If you haven't tried a free email service yet, and you want access to email while vacationing, take time to read about and try out some of the free services available.