>>We specifically don't want to create accounts and have to manage them. We'd like users to be able to submit comments and require only an e-mail for confirmation. It's unlikely any single user would comment more than once or twice; if anyone becomes a "frequent commentor" I suppose we could have an optional registration which could save those few users some time.
>>
>>Another general possibility would be use of captchas but an e-mail actually works better for our purposes.
>
>In such case, you might apply first level email validation followed by a more robust email validation, which could include the send of the email as you mentioned. But, for that, you would need to implement some kind of pending mode for those messages to not be posted until you have something that confirms it would be ok. Then, you would have to decide how long you would like this robot application to wait for a rejection of that email, if it happens, before taking the decision to accept the message. So, using that route means that the message wouldn't be posted right away. In environments where no registration is applicable, you would end up with that concern and there is no easy way to workaround that.

Thanks, this has helped clear up my thinking on this topic. As you point out, I think it boils down to the job of handling registrations up-front vs. the job of handling pending/unconfirmed messages.

I was initially thinking that getting a success/fail result from sending an e-mail would be nearly instantaneous. However, now that I think about it I once set up a mail server myself whose polling interval is 1 minute, so getting a response from that one could take at least a minute. So yes, the problem of pending updates is real.

I think we may end up requiring registration for those (relatively few) users who will want to post comments. If they don't want to comment, they don't have to register.