Sometimes you may experience problems sending or receiving mail because the IP address that your ISP has given you is listed in spamming block lists. This isn't your fault, and if you are listed, just disconnect from the internet (eg, turn off your ADSL router or your mobile phone), leave it five minutes and reconnect. You should then be allocated a new IP address.
You can use the tools below to check if your IP is listed as a sender of spam.
All of these links open a new window.
Check at SpamcopA great list that catches out a lot of spammers - very reliable!
Check at SpamhausWe use their Zen list which is a combination of all the Spamhaus lists.
Check against every listDNSBL have a great site that checks every blocklist around the world.