You can create Custom Labels for use within Redtail, but these will show up in the Mail Merge menu on your Advanced Search page, rather than in the Labels menu. If what I am doing does not help then I have no clue what's wrong. The Label choices are the same for the rest of the Label style numbers. You can also change these values right there in the envelope feature without having to mess around with styles and templates, but I think this is not actually working for you and I have no idea why not.
Unless I am using some other template with these styles (i.e., styles with the same name), these will be the defaults whenever I run the Envelopes feature. (Open normal.dot, go to Format, Styles, change List to All Styles and insert the style you want, modify it as desired and save the document as a template) These fonts are quite different from those for my business letters. I also added Envelope Address and Envelope Return to my normal template. Note: You can also use Envelope Return if your envelopes are not printed with your return address.
When I compose a letter using this template and have it open, I highlight the name and address, click on Tools, Envelopes and Labels, select Envelopes and the text is entered in the desired font with all the other characteristics I wanted. If you want to create a customized envelope, whether for personal or professional use, but don’t want to invest the money having it done professionally, Microsoft Word has you covered. Place the blank envelope in the printer tray, according to the diagram in the Feed box. Go to Mailings > Envelopes, and enter delivery and return addresses.
I set the font and paragraph details in that style. Word gets information from your printer and shows you the right feed option. That template contains a variety of styles, including Envelope Address. Word adds the envelope to the current document as. If you want to save the envelope for reuse, click Add to Document, and then click the File tab, click Save As, and type a name for the document. For example, I have a template for business letters (for me: letter.dot). If you want to print the envelope without saving it for reuse, insert an envelope in the printer as shown in the Feed box, and then click Print. If you’re happy with the design, press File > Print > Print to begin the printing process. I don't know if this will help but I have dealt with this problem (in Word 20) by using templates. Word will change the page layout to suit the envelope printing options, adding the addresses on each page.