SortEmailAddressesOLD←{
⍝ Sort email addresses ⍵ first by domain, then by mailbox
⍝ ⍺: Optional unique flag
     ⍺←0 ⍝: Default, return all addresses
⍝    ⍺←1  : Return unique email addresses (case-folded domains)
⍝ ⍵: Character vector with embedded new line characters
     admat←↑(⎕UCS 10 13)((~∊⍨)⊆⊢)⍵ ⍝ Split by new line
     dnorm←⎕C 2⊃↓⍉'@'(≠⊆⊢)⍤1⊢admat ⍝ Normalise domains
     dgroup←dnorm(⊂⊢)⌸admat        ⍝ Group addresses by domain
     dsort←⊃⍪⌿{(⊂⍋⍵)⌷⍵}¨dgroup     ⍝ Sorted within domain
     dnorm←⎕C 2⊃↓⍉'@'(≠⊆⊢)⍤1↑dsort ⍝ Normalise sorted domains
     sea←(⊂⍋dnorm)⌷dsort           ⍝ Sorted Email Addresses
     ⍺:sea⌿⍨≠⎕C@(∨\'@'∘=)sea       ⍝ Unique only
     sea
 }