Attachments names are changed in outlook 365 when names are long

Hi Monferrato,

Many thanks for your updates in private message and here, and I am sorry for the delayed reply due to out-of-office, I have tried to send the attachment from Outlook and receive it in Outlook, but the issue doesn't appear. Based on your sharing, it seems that Thunderbird encodes file with RFC2231, since we are not familiar with Thunderbird, as for details about Thunderbird, please contact Thunderbird for confirmation, your understanding is appreciated. If the Thunderbird client that you use does encode file with RFC2231, yes, you are right, RFC2231 encoding should be root cause of the issue, as what you have searched, Outlook Insider product has fixed this issue while Outlook of current channel doesn't have related update, I'd like to share with you that any updates of Office products are first released to Office Insider product, in which user could experience richer feature, it is actually a beta Office product, after feature is updated in Office updated, in general, its most feature will be updated to the related Office of current channel that has same product number in the next period, I have just compared Office Insider and Office of Current channel product, the Office Insider product(Version 2006 (Build 13001.20002)) that has the RFC2231 issue fixed doesn't have corresponding Office of Current channel product, so this fix may not be released to common Office product yet, at present, please temporarily shorten the file name to work around this issue, or you could try to zip the file or put the file to a folder , then view if it helps. As for the fix for Outlook of Current channel, we recommend you could post using feedback to our dedicated Outlook uservoice, our development team is there, and after they notice your feedback, believe they will consider to update this feature, thanks for your cooperation and understanding.

Regards,

Betty