Correct SMTP settings for gmail to do "Send as"?

I am new to using webmin/virtualmin and I have setup a few virtual servers using virtualmin. I have user accounts on those virtual servers that I forward mail to gmail from. In gmail, I wish to setup a “send as” to use those domain accounts emails. I’ve been unable to get gmail to connect via TLS. Can somebody either tell me what the correct settings are on the virtualmin side or point me to online documentation that has examples?