We have an OSTicket system that's been used for several years. It's currently at 1.15.6. 
The default email to which clients can send a support request receives and processes attachments as intended. We added another email to capture a different group of support requests, but that email cannot pull ZIP attachments into the ticket. I can add attachments to those tickets via the web portal. I've tested this from multiple source email systems (MS and Google). There's no errors in the OSTicket log and nothing of consequence in the server logs.
The following errors are displayed in the ticket:

Server Information
osTicket Version 	v1.15.6 (1a64b84)
— v1.15.8 is available
Web Server Software 	Apache/2.4.41 (Ubuntu)
MySQL Version 	8.0.29
PHP Version 	7.4.3
PHP Extensions
gdlib 	Used for image manipulation and PDF printing
imap 	Used for email fetching
xml 	XML API
xml-dom 	Used for HTML email processing
json 	Improves performance creating and processing JSON
mbstring 	Highly recommended for non western european language content
phar 	Highly recommended for plugins and language packs
intl 	Highly recommended for non western european language content
fileinfo 	Used to detect file types for uploads
zip 	Used for ticket and task exporting
APCu 	Improves overall performance
Zend Opcache 	Improves overall performance
PHP Settings
cgi.fix_pathinfo 	"1" is recommended if AJAX is not working
date.timezone 	America/Chicago
I'm at a loss. This only occurs with the new email address being added. All settings are the same as the default address.
 
Any suggestions?