Do Yahoo e-mails get delayed for insufficient postage.?

Lately, my Yahoo e-mails have suffered 4 day delays before I get them. I have twice read e-mails to see one sent prior arrive behind those. And today, I went back and found a couple new e-mails from tuesday that weren't there last night. Not to mention that one person I write to sends numerous e-mails tat never arrive at all and violation warnings if she sends e-mails too often to my other two e-mail addresses outside Yahoo. Pretty strange! And I am relatively familiar with computers, having worked with them since 1965. Trained on the IBM PC-XT, HPs, Compaqs and Northwest to repair them at component level., familiar with machine, embly, Fortran, C, HPL, Unix, Sun, Pascal languages and programmed with them. Has every indication e-mails are falling into exception codes or continuous loop vortexes..