We have seen a large number of cases where parties have come to grief by attempting to serve by email in circumstances where the other party has not consented. There is a petition to amend the rules.
PRACTICE DIRECTION 6A
This Practice Direction has a specific section on service by electronic mean...
Here is the link for anyone interested: https://www.change.org/p/civil-procedure-rule-committee-consider-implementing-electronic-service-as-a-primary-service-method-in-civil-proceedings
One concern that isn’t mentioned here is the cost: if a document is served by email (and regardless of the emphasis on paperless offices) it is more likely than not that the recipient will have to print it out. This puts the cost on the receiving party which should belong to the sending party.
For many firms and others involved in litigation this will be a swings-and-roundabouts issue, where they lose as often as they gain. But there may be others for whom it is a potential problem.
I once had to deal with a Particulars of Claim from an LiP which was 65 pages long. Good job it was in small font and closely spaced with small margins otherwise it would probably printed out at more than 250 pages…