Email send fails with error "com.sun.mail.smtp.SMTPAddressFailedException: 452 4.5.3 Error: too many recipients" in system logs.

Symptoms

• Email send fails with error "com.sun.mail.smtp.SMTPAddressFailedException: 452 4.5.3 Error: too many recipients" in system logs.
• The email in question is set to Send-Failed.
• The number of email recipients in the email is greater than 1000.

Please note that this is applicable only in cases that have custom scripts that use GlideRecord to create email record and passes email addresses to the To: field. In this case, the script bypasses the recipients per email functionality defined by 'glide.email.smtp.max_recipients' in any other way.

The ServiceNow email server limits a single email's recipient count to 1000. The property glide.email.smtp.max_recipients should never be set larger than the number the mail server can support, which in the case of ServiceNow is 1000. 

PLEASE NOTE: Scripts fall under customizations and are beyond the scope for ServiceNow Support to troubleshoot/improve.

Here are our recommendations:

1. (Recommended) Explore using the GlideEmailOutbound object instead of GlideRecord in your script since it should respect the system property glide.email.smtp.max_recipients and split the needed emails. When calling GlideEmailOutbound.save() to send the record, the chunking will be handled automatically for the emails. 
2. Explore using the system property glide.email.smtp.max_recipients in your script and duplicate this splitting functionality in your custom code to ensure any single email's recipient count does not exceed the property value.