We had a question regarding this via TT#40297.
There is too much risk in doing this for a customer who has so many e-mails and who cannot afford to lose any of them. Also if they are concerned about losing their e-mails we would hope they have a backup in place and it is OK to mention that. We do have online backup services available.
We can do this copy over via screen connect for customers who we change from POP3 to IMAP if they only have a few e-mails. Otherwise it is a clean slate with the IMAP setup unless they want to move their data on their own or hire a computer technician to do it for them.
If they do get someone to do it for them it should be noted that they do not have to stay within the 1GB @hay.net storage limit. Getting into more storage that 1GB involves more though such as a) sigh up for a web hosting package, b) get a domain name and setup e-mail. Web hosting packages start at 2GB and go up to an incalculable number that in theory exists but is incomprehensible.
Thank you so much for asking about this and not diving in to do it head first. It was good judgement and in the case of this ticket I will contact the customer and explain the best options.