If you have problems with Siteground emails going into spam / junk folders adding a DMARC record in Siteground Site Tools can help.
Setting up a DMARC Record on Siteground Web Hosting
Site Tools > Domain > DNS Zone Editor
Add the following TXT record
Value: v=DMARC1; p=none; rua=mailto:firstname.lastname@example.org
This will need to be repeated for each email address.