Please check your emails (both body and signature) for spammy content e.g. lots of exclamation marks; "must read"; attention-getting, large and/or gaudy coloured text; text the same colour as the background; tiny text; [almost] zero height images; links hidden under text, images or links with a different URL; etc.
All or any of these may mark you as a spammer at Google.
Changes to MX records may take up to 72 hours to filter through the Internet;
We cannot help you with these issues, which need to resolved by yourself, or with the assistance of an IT support team.If other Google users have marked your mail as Spam, Google will have learned from this. You need to get your mail marked as "non spam".
If your IP is marked as a Spam Hoster, you will also need to clean this up with your service provider. Google maintain their own lists, but this posting certainly cannot help you. Removal from a spam hosting list can take up to four weeks to filter through. Even after that, Google may treat you account very cautiously, until proven as non-spammer.