mobile email; email from a cell phone
Extremely rare term; modern Japanese uses 携帯メール or スマホのメール. This appears to be an obscure or obsolete compound.
See also: 電郵
The word 携帯電郵 is hardly used nowadays.
Compound of 携帯 (mobile) and 電郵 (email, itself an obsolete abbreviation of 電子郵便). The exact origin is uncertain, but it likely appeared briefly in early mobile internet contexts.