The email sent to update/create tickets (Mailbox) need to be sent in plain text format. If they are sent using HTML format, the content is not processed/parsed but attached as it were an email attachment.
Maileater does not appear to work well with HTML formatted emails, is it supported to use HTML emails with maileater?
Windows, Maileater, Service Desk 12.X 14.X, MS Exchange
Users do not need to be forced to create plain text emails to create/update tickets. Instead, the account associated with processing Service Desk emails (the email account configured in Mailbox settings) may be configured in mail server to accept mail (IMAP or POP3) as plain text.
That way even when the user that attempt to update/create a ticket, sends an email using HTML format, the Service Desk email account configured in mailbox, will receive an email in plain text, and it will be able to process it correctly.
This, however needs to be configured in mail server. Basically, you may force the mail server to process the incoming mail, and be presented to the recipient account you configured in the mailbox, as plain text.
In Microsoft exchange for instance, this is named as Content Conversion. Please consult your Mail Administrator how to configure this in your Mail Server.
Be aware that still maileater process require the format of the mail received be in plain text. Following this suggestion, you are just configuring the mail server to convert the mail from HTML format to plain text, before to send it to the recipient (Service Desk mailbox account)
Content Conversion Exchange 2013
How to Configure the Mailbox to Handle Inbound emails