1. Use the search options or look under the bugs forum, there are a gazillion posts about this topic and it usually relates to an improperly configured mail file. Details
can be found in those posts as to how to configure it properly.
2. I'm not too sure there is much tweaking you can do to yaf itself off a fresh install. From my experience this sounds like an issue with the server. General system performance improvements, sufficient memory etc, could help. Others might have a suggestion I haven't considered, sometimes it can take a day or three.