I have recent issues regarding Bad outgoing attachments Office 365 in Thunderbird. I always sent correct attachments with Thunderbird to mail client like Lotus Notes, or IBM Notes. Recently some workmates moved to Office 365 and, when I send them some attachments like pictures, they visualize badly because the original attachment arrives slightly bigger in size respect.

To the original: in some points of the original file is inserted in the byte ‘0xD’. If the same file is sent to Office 365 from Gmail, the attachment arrives identical. Reading some forums I tried to change some points of the Configuration Editor but no result is founded. Bad outgoing attachments Office 365 in Thunderbird.

Update Thunderbird settings for Office 365

1. Launch Thunderbird.
2. On the first launch, you may be prompted for your password for your email and
Click Cancel.

3. Mac Users: In Thunderbird, Click on Mail menu, It will show in the upper left corner, next
to the Apple icon.
Click the Account Settings

Windows Users: Click on the Thunderbird Menu button
Click Options then Account Settings.

4. For your email account, click Server Settings.

5. Under the Account Information tab, change the following settings:
a. Server Name: outlook.office365.com
b. User Name: Your full Primary email address,

Note: You can confirm your primary email address in the HMS White Pages.
6. Click OK

7. Click on the Outgoing mail Server and select your HMS outgoing mail server then, click Edit.

8. In the Settings window, change the following settings:
a. Server Name: smtp.office365.com
b. Port: 587
c. Connection security: STARTTLS
d. Authentication Method: Normal password
e. User Name: Your full Primary email address, usually in the form of
firstName and lastName. i. Log into ecommons.med.harvard.edu
ii. Click on Preferences
iii. Then, Click  Messaging
iv. Your primary email address appears under the “E-Mail Options” heading

9. Click OK

10. Click OK again.

11. The first time you Send and Receive email, you will be asked to enter your HMS
password.

Thunderbird is now configured to connect to the Office 365 email system.