To export IMAP emails, trust on the CubexSoft IMAP Backup Tool that is a reliable utility to export unlimited IMAP emails to local system and webmail apps. Using the software, you can powerfully export multiple IMAP email account data in single round processing. The software supports to backup IMAP emails to PST, EML, MBOX, PDF, OLM, EMLx, HTML, RTF, DOC, Gmail, Office 365, IMAP Server, IBM Verse, etc. You can also export selective IMAP account emails with its multiple filters. 

Download IMAP Backup tool and export 25 emails from IMAP account to new computer webmail app and file format at free of cost. Therefore, just try the tool and clear entire doubts for IMAP backup at free of cost. https://www.cubexsoft.com/blog/import-imap-into-office-365/