Problem sending gmail messages from icloud

I have four accounts linked to my icloud mailbox. One mac, two gmail, and one school address. (none are only on my mac - all are online) When composing messages (in compose or reply), icloud allows me to toggle and select any of the four accounts in the "from" section, but will actually only send messages from 3 of the accounts. It never sends from one of my gmail accounts. If I select that gmail account, it sends it from the other gmail account. When I go to the actual google mail site, I have no problems sending from either account. I am receiving all of my messages correctly in all four of my icloud inboxes.

The outgoing mail server, mailbox behaviors, and advanced settings are identical for both gmail accounts. The addressing: "send new messages from" in the composing section indicates the gmail account that will not send.

How can I send messages from my gmail account?

Thank you for your help!

Lindsay