Where the Letter E Breaks the Pattern
Most mathematical styles run A to Z in one unbroken block, but not all of them for this letter. Script capital E is โฐ (U+2130, Script Capital E). Script small e is โฏ (U+212F, Script Small E). These were added to Unicode in the Letterlike Symbols block years before the mathematical alphabets, and the later block left a gap there instead of duplicating them. On some devices a different font draws these characters, so a word set in that style can show one letter that looks slightly unlike its neighbours.
Small Capital, Turned and Other One-Off Forms
Small capital E is แด (U+1D07). Like most small capitals in Unicode it was encoded for phonetic notation, not as a font feature, which is why small caps text pastes as ordinary characters. Upside-down text uses the turned e, ว (U+01DD). Superscript e is แต (U+1D49). Subscript e is โ (U+2091). The regional indicator ๐ช is half of a flag: two of them in a row turn into a flag emoji when they spell a country code.
Which E Is Safe to Paste
Bold ๐, italic, sans-serif and monospace forms display on nearly every phone and computer. Circled โบ and fullwidth ๏ผฅ are also widely covered. The squared and dark squared forms of E have no emoji version, so they stay black and white. Screen readers may announce a styled E by its full Unicode name or skip it, so keep anything important in plain letters as well.