OK, Meds, make a text file with the email addresses of the contacts you want to inform. Just go to your contacts file, folder or wherever and copy and past their email addresses as a single line or lines into notepad or similar. Separate each one with a semicolon and space e.g.:
jon@gmail.com;
dave@bt.co.uk;
bob@outlook.com;
jean@talktalk.crap;
sally@zoho.com: and so on.
Split the big list into line blocks of about ten on different lines so that you do not get picked up for spamming as so:
Line block1
emailaddres@1; emailaddres2; emailaddres@3; emailaddres@4; emailaddres@5; emailaddres@6; emailaddres@7; emailaddres@8; emailaddres@9; emailaddres@10;
Line block2
emailaddres@1; emailaddres2; emailaddres@3; emailaddres@4; emailaddres@5; emailaddres@6; emailaddres@7; emailaddres@8; emailaddres@9; emailaddres@10;
Line block3
emailaddres@1; emailaddres2; emailaddres@3; emailaddres@4; emailaddres@5; emailaddres@6; emailaddres@7; emailaddres@8;
Create a new message and in the To... field put the first address from the line. Now go to the Bcc... field and copy and paste the rest of the line block addresses there. Then complete the Subject field. See below.
My subject line is 'Change of email address' but you can choose anything suitable. Somewhere in the body of the text you should give out your new email address and ask people to respond to it asap, any that don't can then be contacted individually as normal.
You can use the same message over again just by clearing out the To... and Bcc... fields and entering the addresses from the next block as you did with the first, and so on.
I am suggesting Bcc over Cc because there might be some contacts who you do not want to know who your other contacts are. Each recipient from the Bcc field will only see it as being sent to them... so it's a bit more personal.
Bcc = Blind carbon copy
Cc = Carbon copy
ETA on some New Message frames Bcc might no be visible. If that's the case go to the View menu and give it a tick.