Here are the most common problems you can face collecting subscribers and sending newsletters from your WordPress site.
Note: since February 2024, Gmail and Yahoo mail services announced new requirements for senders.
These new requirements for bulk senders (those who send more than 5,000 messages to Gmail or Yahoo addresses in one day) need to be satisfied or it may result in rejecting message delivery to their customers.
Read more on SPF, DKIM, DMARC dedicated page.