for a while we decided to use another Server (VServer "B") for our Mailserver. I transfered all E-Mail Accounts and E-Mails etc. to that Server from VServer "A". VServer B runs well and the clients are getting theyr emails from this server. All emails that come from external SMTP-Servers are received by VServer "B".
Currently I operate two vServers. A small Digital Ocean (vServer1) Ubuntu Droplet serves my Wordpress blog and other PHP applications. On a second, more potent Ubuntu vServer (vServer2) from a different provider I run my subversion repository and I store some more or less critical files. The reason why I separate the two machines is that I do not trust PHP.