Yahoo e-mail suspended for unusual activity?

I send myself e-mails to keep some files available in my mail box to access them where ever I am and also to save disk space since there is no storage limit now, I send 4 or more files daily, but every time ( after I have sent 3 or 4 files no bigger than 1.5 kb ) yahoo suspends my mail because "unsual activity detected" and to protect me and my account they don´t let me send, receive or save anything for 48 hours, what can I do, are they right to do that? Am I going to have to ask for permission or let them know in advance every time I send an e-mail? has this happened to anyone else?