Hm.... GoDaddy. Okay, I guess. Not something that I would ever recommend but let's work with what you've got.
You can get a VPS w/2 Gigs of RAM and between 80 and 180 Gigs of storage from excellent hosting providers for about $7.00/month. GoDaddy I think would charge about $55 or more per month for a virtual machine with only a gig of RAM and 30GB of space, or something along those lines, with a Plesk or WHM/cPanel control panel, if I'm not mistaken, but anyway, get a VPS and install OfflineIMAP and connect ALL of your email clients to that. Have OfflineIMAP connect to all/any of your mail servers and apply your filtering, Antivirus scrubbing, and sorting of email messages into folders there. This way, your clients will all have the exact same message boxes whether on a phone or laptop/desktop.
I Recommend Thunderbird and Lightning for MUAs (email clients), and if you insist on directly connecting to Exchange services then here is the link to the Exchange Connector for Thunderbird: https://github.com/E...xchangecalendar- This will allow and provide for your bidirectional sync for Calendars. If you're also using any sort of Google Calendars, there is a Google Calendar provider you can search for in Tools ==> Addons in Thunderbird.
NOTE: The current version of Thunderbird has Lightning fully integrated and also with CalDAV and CardDAV suport.
Now, you like Ubuntu, Fair enough, although I prefer pure Debian or Slackware. Regardless, setting up OfflineIMAP should not be any sort of issue for you (And if you like, you can actually set it up on your workstation, if that is the only place you access your mail, if not, then put it up on a VPS in the cloud so all of your devices can connect to it.
On your local workstation (if it's windows), I recommend BitDefender in combination with MalwareBytes, but Bitdefender by itself does a pretty good job. If you want free, then Avast (not as good as BitDefender) is decent and I would definitely install MalwareBytes (Premium trial is available, after that you need to manually scan periodically).
I'm not going to recommend any hosting providers for VPSes, since that's the business I'm in, but you can look over at https://lowendbox.com/and vet the providers yourself based on ratings, etc. - there are great, longstanding and solid providers and there are fly by night, here today, gone tomorrow providers - YMMV. I recommend that you purchase a VPS that is either Xen HVM, Xen PV, or KVM - Stay away from any VPS that is OpenVZ or Parallels (Like what you will get from GoDaddy, by the way).
Since your already familiar with running Ubuntu Linux, I assume you're also familiar with the excellent antivirus offerings available to you under Linux for free.
Now, messages from the Mailer Daemon don't necessarily mean viruses - these can be messages for a myriad of SMTP situations including bounces, etc. Always inspect your headers, and on your MUA (mail client) disable remote images/content - Thunderbird does this by default, and if you know it's not malware then you can select to view the images, etc., on a per message basis - this prevents a lot of the mailchimp/constant contact/other services from being able to confirm that you have actually opened the mail and prevents SPAMmers from knowing that they have reached a live email address too (by encoding the URLs of the images and cross referencing the email addresses they send to in a database).
On older versions of Windows, I also often recommend SuperAntiSpyware and cCleaner - but I'm not convinced this will provide any extra protection for you on a Windows 10 box at this time, and bear in mind that Win10 sometimes has a tendency to BSOD when you add additional protections - IMPORTANT: Make sure that your Windows Defender, at least, is completely disabled (It should happen by default when you install Avast or BitDefender but make sure anyway) - this can wreak havoc on your performance if another AV is running on your box.
If you've got any other questions or concerns I'll be happy to give you my spin on them, but always STFW and read the manual too, and I'm sure you will, coz you already run a Linux workstation so kudos and good luck to you!