Hello

sorry, there is nothing that can be done at the Thunderbird level. Thunderbird is an email client. It is connecting to your email server and sending to it your message. Your mail server is then trying to connect to your correspondent mail server - here Hotmail (Microsoft). This mail server is denying your mail server because it don't like its IP address. Your mail server then reports back to you that it did not go so well in the message you received. So you should contact your mail server management, probably your internet provider. They have the problem, not you. Usually other people are also reporting their problems and the problem seen to fix itself after some time (because people have complained and the internet provider network managers have managed the problem)

Hi, I had/have the same problem. "Undelivered Mail Returned to Sender"

Try sending your emails for affected email addresses via your 'webmail'. That works for me, it's a workaround, not a fix. Extra work but gets there.

Optus ignoring the problem. I've wasted 3 hours online with Optus over the last 4 weeks.

Bye Peter

@fhingers (and peter)

this is a fairly common problem happening with people using Microsoft servers. Basically MS is using a 'protection' system that just blocks part of the Internet as 'unworthy' and it's the said part to do the job of appearing 'worthy'. Usually the problem comes from mail servers that are done on the cheap with cheap providers and they are part of a Internet address range where there are spammers. As the cheap providers are not fast enough to removing the spammers, the whole Internet address range is blocked. This is 'collateral damage'.

Thunderbird as an open source project has nothing to do with the Spam policy management of Microsoft, and also with the general Internet management of your provider. The problem is between the mail server of your provider and the mail server of Microsoft.

I'd say that short of forcing Microsoft to behave in a more civilized way (banning only the actual culprits, that would cost of course them more), a solution that is probably beyond what you can achieve, a better way is to use a better behaved mail server. The use of the mail server of your provider is given away 'for free', that is, it's included in the contract. Alternatives are more complicated and possibly expensive, that is:

• using a better internet provider - depends on your place it can be difficult
• using a mail provider unrelated to your provider - requires you (probably) to change mail address and possibly pay an additional sum of money. Do an internet search for 'free mail provider', or 'cheap mail provider'. All these guys are providing specifically a mail service, so they have a clear interest to keeping their mail deliverability at a high level, contrary to your internet provider that has other priorities.