K9 mail problem need help

[Mwsr]

Ok so I seen that a lot of people are using this so I got it a few days ago. I added a aol acc then and it works great. Yesterday I added a yahoo acc and its not pushing my emails through on that one. I deleted that acc and installed again and still same issue. If I go into it and actually hit check mail it will my emails but no push like with the aol acc.. any help appreciated. .

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