Add x-resend-force-plain(-cc) keywords
As discussed in #54 we should add a X-RESEND-FORCE-PLAIN keyword. For the fun, we can can also add a X-RESEND-FORCE-PLAIN-CC variant.
As discussed in #54 we should add a X-RESEND-FORCE-PLAIN keyword. For the fun, we can can also add a X-RESEND-FORCE-PLAIN-CC variant.