You may create an email signature to make your emails more professional.
It can be done in Spacemail webmail: go to Settings, then on the Signature tile, click Manage signatures.

A new page will appear. Press + New signature, input its name (e.g., signature1), and then press Enter. After that, input your signature text in the text editor.
It is possible to format your signature using undo/redo, font and size changes, bold, italics, underline, strikethrough, as well as tools to insert images or links, change text and background (highlight) color, create bullet and numbered lists and apply left text allignment. Additional tools under the arrow include other alignment options, tables, and clearing formatting.

You can choose to make this signature a default one (in case you need several) by clicking the checkmark below the editing field. You'll also be able to do this later from Settings.
Once a signature was added, you will see a pop-up notification that a signature was saved.
NOTE: If you use any email client or apps for sending emails other than Spacemail webmail, you will need to set up your signature in these third-party apps separately, as they do not sync via IMAP.