The only way to disable a SMTP is to delete it.

It would be nice to have a method of temporarily disabling a token to stop its use for sending mails OR any mails received from a specific token user can be temporarily redirected into a black hole like /dev/null.

What is the need.
An application or a server that is setup to mailout with a token could go rogue and spew out a lot mails. Configuring postfix with a token on a linux box gives users freedom to do want they want with the built-in mailers like sendmail and mailx. I've seen a production system rendered useless because of mail services going rogue.

When a token user goes rogue you haven't a clue where the mails are coming from. There is nothing in the mail client to monitor the actions of token users, its only for devices that use the account passwords. There is nothing in the innards of .eml file that indicates a source of the problem. The only forensics you have are the contents of the mail message and there may be no clues in them. It would be nice to have some monitoring.

If you are unsure what token is spewing out all the mails you have to delete tokens until it ceases. All deleted tokens require all the apps to be reconfigured with new tokens. Not a good idea in a commercial environment.