Be Broadband users are to lose their web hosting and email addresses this summer.
Sky - which took over Be last year after acquiring O2's fixed-line business - is to shut down both services at the end of July, meaning all email addresses ending @bethere.co.uk will cease to function.
"This closure will impact you whether you use webmail or a mail client, such as Outlook," Sky stated.
"Please note emails sent to your @bethere.co.uk mailbox will not be forwarded after this time even if you have set up auto-forwarding."
As such, Sky is urging Be customers to update any accounts that use these addresses.
"The sooner you start, the sooner your contacts will know your email address is changing and can make any necessary arrangements,” Sky stated.
The broadband provider says email users may wish to set up an auto-forwarding function once their new email address is in place.
This could run in parallel until the end of July, catching any email from contacts not aware of the change.