I have a domain name hosted at OneandOne.co.uk with a redirect set up so that all email sent to firstname.lastname@example.org gets redirected to my Plusnet mailbox.
When I send an email from Plusnet I've set the 'from' address and the 'reply to' address to email@example.com. Everything seems to work fine at the moment but I'm a little worried about the possibility that some mail servers might reject my emails? I read somewhere that some mail servers check incoming mail to see if the domain in the 'from' address is the same as the domain that sent the email.....or something like that! Is this true or have I misunderstood? If it is true, then are there many mail servers that do this? Should I be thinking of getting Plusnet to host my domain and start running my own SMTP server to send emails?
All I can tell you is that I send mail via Plusnet for two non Plusnet domains & I have never had a problem yet.
You may be able to avoid the re-direct as well. If the incoming mail is to a POP3 server, you can set your mail client to retrieve it directly. You will need to ensure that anything@ mydomain.co.uk is picked up by collecting firstname.lastname@example.org, but that applies whether you collect the mail via Plusnet or direct from OneandOne.
I only mention that because I got caught once - I had a series of named mailboxes on a Freeserve account, & it was a long time before I discovered that any mail to a username other than the named mailboxes was not being collected by the default username. It was only when I used their webmail service one day that I discovered about 2 years of 'anything@' mail still sitting there. As you would expect, it was mostly junk, & mostly from Freeserve themselves!