I organise my calendar appointments through an Android mobile phone using a Gmail account.
One of my projects uses Microsoft OWA, which my phone does not sync with.
To avoid missing OWA calendar appointments, I need to get them into my Gmail account.
There are various on-line services that require me to divulge my OWA username and password. I’m uncomfortable with that. Besides which, our standard company contract prevents us supplying secure access details outside of the company so releasing secure information for a 3rd party to store ‘in the cloud’ would break it.
I solved this by running an exchange gateway (DavMail) on my PC, enabling an email client (Thunderbird) to connect to both Gmail and OWA. I then used the email client filters to copy OWA mail into the Gmail IMAP account. Fortunately when Gmail syncs with my phone, the calendar requests are compatible so seamlessly appear in the my calendar, along with the email.
The downside is that DavMail and Thunderbird have to be running on my PC. However, it gives me total control and is a small price to pay for not missing meetings.
For config details see my blog.