Contact users with active problems/campaigns to inform them of shutdown

[abibroom]

• [x] @crowbot to produce a list of email addresses
• [ ] @abimysoc to organise the mailing

[crowbot]

Problems created in the last six months, all campaigns ever.

[abibroom]

I have tagged in @MyfanwyNixon on the mailing, on the realisation that I will be on holiday when it needs to be done.