We use a third-party provider to handle outbound SMTP transactions - MailChannels: https://www.mailchannels.com/
Their platform doesn't natively support DKIM (it does support SPF however), but similarly, we've seen no foul consequences of that fact. Email delivery via MailChannels has always been excellent.
There is a workaround for that, though - we can exclude your account from MailChannels if DKIM is definitely required, which would enable you to use DKIM, however, we would not suggest this as this would likely result in worsened email delivery rates.
