Technicians have been "working around the clock" to fix problems with the Manx.net e-mail system.
Manx Telecom says it believes it's made "significant progress" after issues transferring 30,000 user accounts, and millions of mail items, to a new platform.
It's described the issues as "unforeseen difficulties" and has apologised to customers who've been affected.
Chief technology officer Kevin Paige says the problems started during the migration process:
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