Fix Office 365 Email Sync

My Office 365 mailbox is no longer syncing across devices and I need a specialist to get it working smoothly again. I have already created the account, but something in the configuration is clearly off, as new messages appear on the web yet never reach Outlook on my laptop and phone... (Budget: £20 - £250 GBP, Jobs: Microsoft, Microsoft 365, Microsoft Exchange, Microsoft Outlook, Office 365, Technical Support, Troubleshooting, Windows Server)