> > Look at grey-listing as well. It should be useful if it can distinguish > > between the user's MUA (or private MTA) and a bot.
MUAs generally don't cope well with greylisting, as they lack good mechanisms for automatic retries - so I'm not sure that's a good advice. > > Why on earth not? You control T&C for your ISP and can change them. If > > necessary you can keep existing charges for authenticated connections > > and raise them for those who don't convert. > > My english is not good enough to understand this sorry :p T&C = terms and conditions. It's your call to set rules of the game. Tell the clients that for a little effort on their part turning on the SASL authentication and submitting through standard mail submission ports, they will be gaining a better service with more reliable acceptance rate by their recipients. Here is another good incentive to use a mail submission service of a domain matching their From address: they gain a valid DKIM signature on their outgoing mail. For example: when using a gmail From address it pays off to submit mail to google on port 587 - the message gains a gmail signature. Sending directly from a home or small office machine and using a gmail or yahoo From address is likely to be treated as second-class mail by recipients (not trustworthy, likely to gain some spam score points). The same (but in reverse) applies to outgoing mail using your ISP's domain: it pays off to submit it to ISP's mail submission service, this is the only way to gain its DKIM signature. Increasing number of domains (like yahoo) treat mail with a valid DKIM signature favourably. Mark
