Here is a workaround.
1 Select the text you want to format
2 cut and paste in a word processor (I use Nisus Pro)
3 Select the text in the word processor
4 Copy and paste the text back into Mail
The line spacing is now manageable and can be formatted.
Hope this is of use
MacBook Air (2018 or later)
When you copy and paste the styled text from Nisus Writer Pro 3.0.1 into Mojave Mail, the font is retained, but custom line spacing is lost. I formatted a paragraph of Baskerville text at 14.0 pt, and set the paragraph spacing to 17.5 pt. This was clearly evident in the Nisus document. Whether I copied and pasted this formatted paragraph, or its paragraph style over to Apple Mail, all spacing information, but not the font name, were lost.
I would be curious how you then managed to adjust the spacing on the text in Apple Mail as it has no spacing controls, and using pre-established TextEdit paragraph styles through the contextual menu's Font : Styles… panel — also failed to set the spacing to a previous configured TextEdit paragraph style with custom line spacing.
The challenge you are facing is that the Apple Mail compose window offers a layer of Rich Text (but not RTF) , and beneath what we see, it is all HTML based with likely pre-determined HTML and style sheets to override what we think we have placed on the visual layer.
When you copy and paste the styled text from Nisus Writer Pro 3.0.1 into Mojave Mail, the font is retained, but custom line spacing is lost. I formatted a paragraph of Baskerville text at 14.0 pt, and set the paragraph spacing to 17.5 pt. This was clearly evident in the Nisus document. Whether I copied and pasted this formatted paragraph, or its paragraph style over to Apple Mail, all spacing information, but not the font name, were lost.
I would be curious how you then managed to adjust the spacing on the text in Apple Mail as it has no spacing controls, and using pre-established TextEdit paragraph styles through the contextual menu's Font : Styles… panel — also failed to set the spacing to a previous configured TextEdit paragraph style with custom line spacing.
The challenge you are facing is that the Apple Mail compose window offers a layer of Rich Text (but not RTF) , and beneath what we see, it is all HTML based with likely pre-determined HTML and style sheets to override what we think we have placed on the visual layer.
How to change line spacing in Mail on any Mac running macOS, Mojave
