The spam scanners of all e-mail providers are constantly adapting to the current spam threats. For this reason, there is an increasing number of cases of legitimate messages being mistakenly identified as spam by the recipient.
You can take the following measures to improve the deliverability of your messages:
Add an SPF entry for your domain
SPF (Sender Policy Framework) is a rule in the DNS zone of a domain that verifies whether a message originates from the mail infrastructure defined in it. For more information, see this article.
It is possible to add a record of the type “TXT” for SPF in the DNS zone. If you send messages via Emubox, this guideline will help you.
Follow the recommendations of the e-mail providers
Follow the recommendation of the e-mail providers:
Google: https://support.google.com/a/answer/81126?hl=en
GMX: https://postmaster.gmx.net/en/best-practices
Microsoft: http://mail.live.com/mail/troubleshooting.aspx
Test the deliverability
Test the deliverability of your messages with a tool such as http://www.mail-tester.com/.
Add the e-mail address to the list of trusted senders
To prevent your messages from being mistakenly treated as spam by the recipient's spam filter, the recipient can add your e-mail address to their own list of trusted senders. You can also publish such a request on your website or ask your subscribers/recipients to add your e-mail address to the list of trusted contacts.