3 Easy Steps to Prevent the Newsletter Ending up in the Troglodyte Trash
TL;DR: The single best thing you can do is reply to the email (a simple "Hi" is enough), as per step 3 below. This tells most email platforms that you are interested in emails from this sender. It is worth also doing steps 1 and 2 below and should only take a round or two of your precious time.
1. Mark as "Not junk / spam"
Check your junk/spam folder after subscribing and move the message to your inbox (and don't forget to click the "confirm signup" button!)
Gmail:

Outlook.com:

2. Add us to your contacts
Add the newsletter email address to your contacts.
Gmail - soooo much easier on the browser (don't even try on the app, its harder than a game of mercy with Bigby himself!):

Outlook.com:
Not too tricky on either app or browser. App looks like this:

Or on the browser:

3. Last but not least... Reply to say hi!
The single most effective way is to reply to our email (just say "hi" is fine!) as this tells the email platform you trust this sender.
Well done fair adventurer, you have passed this puzzle encounter and you can continue your adventuring the land of the blog: