The library when used long term leads to a blacklist by https://check.spamhaus.org specifically for Outlook emails.

Replication Steps:

• Enter any outlook business email
• Library tries to connect with MX Exchange of outlook
• HELO is sent as same as MX Exchange of outlook
• Every time an email is validated a different HELO originates from the same IP which is a spam practice

The library should not encourage this behaviour and instead ask to define a HELO with best practices.