Let's see if I can type this again without my touchpad pressing back and the no-cache deleting my post.
I'd like to gather providers opinion on the use of port 25. My impression from the various providers I've signed up to is that there isn't much leeway for SMTP usage or 'perceived abuse' (hence the question), with some suspending your account if it appears on a DNSBL list, some flagging you for using SMTP on any kind of scale. This is understandable and a provider will want to protect their IP space and other customers.
Say I work with a number of small-mid-large sized businesses who have a list of email addresses for their customers. Periodically they'll want to 'prune' the list for unreachable addresses. They outsource this task to someone like me.
The traditional method of cleaning is to contact the SMTP server which can tell whether the address exists or not... without sending an actual email, hence no spam. Server gets connected to, and a RCPT address@address.com is sent with the server giving a response code usually indicating whether the address exists or not. The connection is then closed. It's worth repeating that no email gets sent.
The method has naturally been abused by spammers in the past (who are naturally opportunist), though they tended to forge the from address or send an IP with the HELO greeting rather than a domain. In my case, I'd have reverse DNS configured, and all the appropriate DNS records to show that the originating request is indeed valid.
So my question to providers is, is that an acceptable usage of a VPS in your opinion? Where is the line in the sand for you.
Thanks for your time.