How to Replicate

• Under Profile icon > personal settings > email format- select Text email format
• Add a comment by mentioning any user on any issue.
• User will receive an email where mentions are represented as account IDs and links are represented as plain text
• Tested the same on my instance and for me , mentions are shown as account ID as well but links are shown as hyperlinks when the personal email setting is selected as HTML, if it is changed to TEXT, the hyperlink is changed as plain text.

  Profile icon -> personal settings -> email format - TEXT
  Settings -> system -> User Interface -> Default user preference > Email format : HTML

Actual behaviour

• Hyperlinks are rendered as plain text
• The mentioned user in comment, when an email is triggered if the personal mail setting is selected as Text, the mentioned user atlassian account id is displayed instead of the mentioned display name.

Expected behaviour

• The requirement is instead of switching back to HTML email format, the TEXT email format should not change the hyperlinks as plain text.
• Instead of Account ID, the display name should be visible in TEXT format as well as the AAID is of no use to customer.