The option to “discard” suggested contacts in your chat list is rolling out to users. We will be making further changes to make suggested contacts more relevant for new users in the future as well, so marking as partially completed. Thanks for your patience with this one.
~Alex & the Teams teamTristan commented
The suggested contacts feature is pulling out of date information from somewhere (delve?) - even for internal staff.
That means our users get bounces when sending to our own staff!
Remove this feature - or at the very least, allow us control (eg, update caches) so that it doesn't *break email*