Can´t send e-mail from any provider

[#1]

Have tried 3 different e-mail addresses (yahoo centrum and seznam). My messages are being returned saying that they are spam and that within the last hour I had sent lots of e mails eventhough I hadn´t been online. I called PN and they said I should contact my e- mail provider, which I had already done. They said that it was my IP address that was blocked. PN told me that it wasn´t possible and I should contact my e-mail provider. Now. I am not very technically gifted so would appreciate some help. When I checked if my IP address was blocked it was on 4 relay black lists. Any ideas anyone? thanks

[#2]

Are you sending via the Plusnet relays relay.plus.net or via some other method
Reason for asking is that your IP address shouldn't appear in the email trail or are you trying via the other providers webmail

[#3]

Just logging on to yahoo etc and sending an e mail. Some go and some don´t.
got this on one of the blocking sites
Outbound Email Policy of Plusnet Plc for this IP range:
It is the policy of Plusnet Plc that unauthenticated email sent from this IP address should be sent out only via the designated outbound mail server allocated to Plusnet Plc customers. To find the hostname of the correct mail server to use, customers should consult the original signup documentation or contact Plusnet Plc Technical Support.

[#4]

If you are logging on to "yahoo, etc" that implies to me that you must be trying to use those service providers' webmail systems. In which case I'm puzzled why Plusnet IP policies should be an issue. Or are you not doing that but trying to use those providers' SMTP servers for sending mail?
What's the physical difference between emails that "go" and emails that "don't"?

[#5]

Thanks for the replies. No differnce I can tell in the messages I send, just some get through (but into spam) and some don´t. I am not doing anything different, just trying to use my e-mail accounts. The error comes back message cant be sent 5:7.1. Have typed my IP address into a website to see what the problem is and 4 RBLs say it is blocked

[#6]

If the IP address you've checked is the one Plusnet assigned to your connection (which appears bottom right of your posts), then that will be dynamic and appear as such on PBLs, Policy Block Lists. These are *not* RBLs which are Realtime Black Lists. IPs on PBLs should not be hosting mail servers, which deliver emails directly to an addressee's mail server, Instead mail should be sent through relay.plus.net and those servers are *not* black listed (I've just checked).
What email program are you using and is it configured to send messages through relay.plus.net?