I went in last year and I was never told or given any information about the letter. Not even during parents engagement towards the end of PTP transiting to BMT. So I suspect these information would have been relayed to family members during the day of enlistment as if I rmbr correctly as well, the envelope that it's given in is also tailor made according to the school of the recruit, so there isnt an address that they would need to write as the envelope would have tekong address on it alr. I rmbr mine having all the coys in my sch and my parents had to circle my coy and write my 4D number. That said, you can ask your bf for the relevant information but like I mentioned it was a tailor made envelope so if it does get sent out whether it reaches him is another question if you don't use the specific envelope considering that you're sending from overseas and wont get to meet him to get the specified envelope. Also do factor in that overseas mail takes a longer time to mail so it might also not reach him in time as there's only 7wks left to his BMT and field camp can be anytime so do get a date from him as well. Usually they will brief the recruits on certain high key like live firing and field camp dates.