I get your feelings TTD. Consider which is worse - sending a one line text or having to deal with the toys out of pram tantrum when he eventually finds out about the post.
Send the text, then turn your phone off and don't turn it back on until tomorrow (unless you are expecting anyone else to call you between now and then of course). At least he won't be able to blame you for not telling him about the post.
The other options are to either forward to his new address or return to sender.
You can get over this hurdle TTD. You've got it in to do it .
Both 50 S14 M 16 yrs (his 3rd; my 1st)
ILYBINILWY - 24 Dec 2012 H moved out - 27 Jun 2013 Legally separated - 6 Sep 2013 Closing the door and changing the locks