For automatically inserting date into signature when composing new emails, replying to, or forwarding emails, please do as follows.

1. Click Kutools > Options. See screenshot:

2. In the Options dialog box, please check the Add a signature with date when create, reply to and forward email box under the New tab, and then click the OK button.

Tips:
(1). You can change the signature information on the text box based on your needs;
(2). You can copy one of the date codes from the Usage section to the Add a signature with date when create, reply to and forward email   box.
(3). If necessary, you can click the Date Format button next to the Add a signature with date when create, reply to and forward email  box to change the date and time format in the signature.

From now on, when creating, replying to, forwarding messages, the signature with the current date will be inserted into email body automatically.

This section will guide you to automatically insert date into the subject line when creating new email messages.

1. Click Kutools > Options. See screenshot:

2. In the Options dialog box, check the Add date into subject when creating a new email box under the New tab, and then click the OK button. See screenshot:

Tips:
(1). You can change the subject content as you need in the Add date into subject when creating a new email box.
(2). You can copy one of the date code from the Usage section to the Add date into subject when creating a new email box, such as <<Date>>, <<UTCDateTime>>, etc.
(3). If needed, please click the Date Format button next to the Add date into subject when creating a new email box to change the date and time format in the subject.

When creating new email messages each time in Outlook, the current date will be automatically inserted into the subject.
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Change the date and time format in subject or signature:

(1) In the Options dialog, on the New tab, you can click the Date Format buttons to customize the date time format in the subject or signature.

(2) Now the Date Time Format dialog box comes out, you can pick up the date format and time from both Available formats list boxes, or type in the custom format code into the Custom format boxes.