Hello,
In my case (I want to send a cover letter as I filled something wrong in my application),
I tried the following email addresses, together with the "paid" email enquiry on Home Office's webpage:
ApplyOnlineE-Support@homeoffice.gsi.gov.uk
SRSUKVACS@homeoffice.gov.uk
Yet unfortunately I did not received any useful reply.
Hence I also sent the letter to the postal address:
PO BOX 3468
Sheffield
S3 8WA
This time I got a reply in post, and they said "it's fine, we've added it to your file in the system".
So don't worry, just try to send it out before the case worker handles your case (if you're using the
standard service, then surely your case is still in a very long queue!)