Hi,
First let's troubleshoot in Safe Mode, to determine if it's 3rd-party add-ins related:
Press Win + R and type “outlook.exe /safe” in the blank box, then press Enter.
If there’s no problem in Safe Mode, disable the suspicious add-ins to verify which add-ins caused this issue.
Please disable the security AVG/Firewall, especially the mail scanner module to check if the new incoming emails are good.
If this issue only occurs to certain senders, please visit your webmail site to check the emails, do they still look the same? What type of format are these emails? HTML, RTF or Plain Text?
Regards.
Melon Chen
TechNet Community Support
