I'm transcribing a science book, Nemeth within UEB and propose all electronic addresses to be in UEB. In the past when transcribing entirely in Nemeth all CBC was also Nemeth. But Nem/UEB Guidelines doesn't specify either way. If there is a "rule" about this I can't find it. I hope I'm asking in the correct forum.
You are correct that electronic addresses in a "UEB with Nemeth" transcription should be transcribed in UEB.
The BANA Guidance for Transcription Using the Nemeth Code within UEB Contexts (Approved April 2018) tells us what belongs in Nemeth Code, and electronic addresses are not mentioned because they should be in UEB.