e-mail rejected for spam

[surfweb82]

Hello.

I'm using ubuntu and rc7.

The problem is that many e-mail is rejected because it considered spam.
If I send e-mail from my gmail account that arrive, but if send from the other domains are rejected.

Why? How do I get all the mail?

Thanks for your help!

error:

Recipient address rejected: Mail appeared to be SPAM or forged. Ask your Mail/DNS-Administrator to correct HELO and DNS MX settings or to get removed from DNSBLs; MTA helo: swip.net, MTA hostname: mailfe15.tele2.it[212.247.155.205] (helo/hostname mismatch)

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i send e-mail from katamail, yahoo, gmail and received but another domain not received!!