Hi,
Bluewin apparently has added ip-range restrictions to smtpauth.bluewin.ch so it is not usable anymore from some ip-ranges (like ours and freesurf I was told).
Well, i don't work at Bluewin-Messaging anymore, but:
'Free' (aka non-paying, aka not-verified) customers are not allowed to use smtpauth.bluewin.ch from non-bluewin networks.
We do/did this to stop spammers: Otherwise they'd just register free accounts for spamming.
Your customer has two options:
#1: He can 'glue' his free account to a pay-account
#2: He can call the bluewin helpdesk and tell them to disable the 'iprestriction option' for his mailaccount.
Regards, Adrian