Numverify VS Spam Check

Numverify — Global phone number validation and lookup JSON API. 250 API requests/month. - Source: dev.to / over 1 year ago

As the name implies, phone confirmation APIs are used to verify contact information. Phone numbers are checked for validity and continued use by verification APIs and services (i.e., they exist). They can also be used to identify geographic data and standardize phone numbers for regulatory purposes. The phrase phone verification API is extremely broad. - Source: dev.to / over 1 year ago

This technology can be used in combination with other security measures to further protect your privacy and prevent fraudsters from getting through to you. When it comes to privacy and security, there are a few things more important than keeping your phone number safe. That's why reverse phone API can be such a valuable tool. By using this technology, you can keep your number hidden from public view, making it... - Source: dev.to / almost 2 years ago

Phone Numbers are required by businesses for various purposes as some use mobiles to send out greetings on a regular basis, while others use messaging to market products or services, and still others necessitate phone numbers to provide better service. Therefore for the verification of these numbers, phone number verification APIs are best to validate them. The business can avail the benefits such as saving time... Source: almost 2 years ago

Phone confirmation APIs are being used to validate contact information, as the name simplies. Verification APIs and services check phone numbers to make sure they're still in use and legitimate (i.e., they exist). For regulatory concerns, they can also be used to standardize phone numbers and identify geographical data. Phone Verification API is a vast term in itself. - Source: dev.to / about 2 years ago

You should check to see if the messages that are being sent contain any links that would be considered questionable/spammy. You can also try taking the content of one of the messages and checking it’s spam assassin score ( https://spamcheck.postmarkapp.com ). Source: about 2 years ago

Build a clean email that passes a spam check with flying colors (https://spamcheck.postmarkapp.com/) then use a warmup service like lemwarm, inboxally or neverspam as mentioned in the other comments. Source: over 2 years ago

The issue sounds more email centric. You're likely hitting the Apache SpamAssassin limit on the remote email servers. Use https://spamcheck.postmarkapp.com/ to check the score of emails you've had declared spam, and follow recommendations to improve. Source: almost 3 years ago