Problem

When replying to an email notification from JIRA using Microsoft Outlook client, it adds unwanted attachments such as the footer, issue type icon and etc.

Diagnosis

1. Replying from Gmail account is not adding any unwanted attachments.
2. Replying from Microsoft Outlook client, it is adding unwanted attachments.

Cause

1. If it is the issue type icon, then this is a bug in JIRA and please monitor  JRA-60810 - Getting issue details... STATUS .
2. If it is happening on the footer, radio and etc. PNG files that is being embedded in the email by JIRA, then this is related to:
   1. Image can be rescaled in HTML email by using width and height attributes of an img tag. When replying to such email, Outlook resizes image.
   2. It uses Microsoft Word as a rendering engine, hence the image is getting resized.
   3. Windows OS settings may impact this in regards of DPI.

Resolution

1. There is no workaround to fix the issue type icon since the bug is still under investigation. 
2. If it's all other attachments:
   1. Outlook can be set to resize images as an option - please refer to Reduce the size of pictures and attachments.
   2. Outlook uses IE to render the mail you are reading, you may want to check in IE under Internet Options > Advanced Tab > Multimedia section, and enable/disable the "Enable automatic image resizing" and see if that helps you out - look at the screenshot in Why is Outlook 2007 resizing images in outgoing and incoming HTML email? How can I fix this? for more details.
   3. For the DPI setting - Picture Sizes Differently in Word and Photo Editor.
      
      
       It would the best if you can get a Windows System Administrator to look into these matters since this involves and needs Windows Administrator knowledge.