Depression UK is a national self-help organisation that offers support to its several hundred members. Most suffer from depression; others may be past sufferers, or care for those who have the illness.
The organisation provide information, produce regular newsletters and run a pen friend scheme. Anything they may send to you will be posted in plain envelopes. As they are a volunteer run organisation it may take a few days to reply to emails.
Depression UK also run a membership scheme which costs £10 a year and a number of services are limited to members only.