How to fix truncation of attachment names from emails in Ruby?

Question

Ruby on Rails

The problem is next. A service written in Ruby checks the mailbox.
If he sees that there is a special code in the letter, then he saves the attachment from it to the database.
Sometimes attachment names are truncated. In the logs , in a problematic
case, the name of the attachment looks like this: the encoding tag occurs again at the end of the email because the filename is truncated at that point i.e. to ==?= =?koi8-r?B?IDQ2OC5wZGY=?= Where to dig?