The Rename All utility of Kutools for Outlook can quickly rename all attachments of the current email without saving the attachments.

1. Click the message item which contains the attachments that you want to rename, and then click Kutools Plus > Attachment Tools > Rename All.

2. And an Attachment Rename dialog box comes out. Double click the attachment name you want to rename, remove the original attachment name, and type the new name you need, see screenshot:

Tips: This operation will rename one attachment at a time. For multiple attachments, please repeat this operation as you need.

3. Click OK. Then you can see all attachments of the selected message are renamed in bulk.

Supposing you are composing a new email or replying/forwarding an email in the message composing window, and you have attached files in the email, you can apply the Rename All (Attachments) feature to rename these attached files easily in Outlook.

1. Click Kutools > Rename All to enable the feature.

2. In the Attachments Rename dialog, please double click the attachment name you want to rename, and then type in the new name.
Tips: This operation will rename one attachment at a time. For renaming other attachments, please repeat this operation as you need.

3. After renaming all attachments as you need, please click the OK button to save the changes.

Then you will see all attachments are renamed in bulk in the message composing window. See screenshot:

Note: This Rename All (Attachments) feature does not support to rename attachments in a Rich Text composing message yet at present.