The first part will guide you to change the font size of both message header and username when printing the email in Outlook.

1. Select the email whose message header and username you will print with small/big font size, and click File > Print.

2. Now please specify a printer, select Memo Style in the Settings section, and click the Print Options button. See screenshot:

3. Now the Print dialog box comes out. Please click the Page Setup button. See screenshot:

4. Now you get into the Page Setup: Memo Style dialog box, please go to the Format tab, and then:
(1) In the Fonts section, click the Font button besides the Title box, next in the Font dialog box specify a proper font size and click the OK button;
(2) In the Fonts section, click the Font button besides the Fields box, next in the Font dialog box specify a proper font size and click the OK button;
(3) Click the OK button in the Page Setup: Memo Style dialog box.

5. Now you return to the Print dialog box, you can click the Print button to print the email directly; or click the Preview button to preview the email firstly, and then click the Print button.

Note: The specified font size for both username and message header will be saved and applied to other emails automatically when printing in future.

Easily print an email' message body only without header and username in Outlook

As you know, when printing an email in Outlook, it will print out both of email header and email body as what you view in the Message window or Reading Pane. What's more, it usually adds your username above the message header. Here, I want to introduce the excellent Advanced Print feature of Kutools for Outlook, which enables you to print an email' message body only without the message header and username, and remaining the background image in Outlook.

Above part can only change the font size of fields in message header and the username when printing emails in Outlook. For changing the font size of message body, please do as follows:

1. In the Mail view, double click to open the email whose message body you want to print with small/big font size.

2. Now the email is opening in Message window. Please click Message > Actions > Edit Message. See screenshot:

3. Now place the cursor in the message body, and then select all message body with pressing the Ctrl + A keys.

4. Go to the Format Text tab, and click the Increase Font Size button or Decrease Font Size button to adjust the font size of selected message body. See screenshot:

5. Click File > Print to print the currently opening email. After printing, please close the Message window without saving.

Print emails in chronological (reverse) order in Outlook

Print contacts with notes or contact notes only in Outlook

Print an email including background image/color in Outlook

Print search results in Outlook