I would have translated as follows : A grande surpresa do webmail (ou das contas de email).

See the definitions below.

I hope it helps.

Bye!

Winndfall noun

something blown down by the wind, as fruit from a tree
any unexpected acquisition, gain, or stroke of good luck

windfall Synonyms windfall
n.

boon, stroke of luck, weal, freebie*; see blessing 2, surprise 2.

windfall Usage Examples Converse of object

reap: The Iraqi leadership reaped a public relations windfall last weekend with its deft handling of the hijack of a Saudi airliner to Baghdad.
receive: Bedford has received a windfall to the tune of £ 4 million.
expect: Do n't encourage your heirs to expect a windfall, however.
get: Right now, getting a 2,000 windfall would make me " rich " .

Adjective modifier

unexpected: There had been an unexpected windfall of half a million pounds more in License Fee income than expected.
massive: Sadly, that does n't mean that QPR can look forward to a massive windfall in a few years ' time.
huge: The huge windfall is set to commence late this year with a one-off dividend worth a huge $ 32 billion being scheduled for December.
financial: For example, existing late night operators should gain a financial windfall from reform should the maximum license fee remain around £ 500.
potential: At the time we did not understand the potential windfall that we have come to realize by making this commitment.
big: Adults are covered big windfall for or people moving.

Modifies a noun

apple: All over the ground are the windfall apples we did n't get to collect.
tax: We are pressing for a windfall tax on their profits.
levy: Through the windfall levy, 5,000 schools throughout Britain have already been modernized.
profit: Under oil windfall profits, Russia 's GDP should have grown by 15 % to 16 % in 2005.
saving: And the hypothetical reply is: the hypothetical costs will be paid out of the hypothetical windfall savings.
taxis: A short run benefit of this was another of Brown 's special windfall taxes.

Noun used with modifier

cash: On top they may be due arrears back to last January, bringing a possible extra cash windfall.
pound: Housing windfall for OIC Orkney Islands Council has received a £ 3 million pound windfall for housing.
tax: Two million pensioners will receive a personal phone call telling them they are entitled to a £ 50 monthly council tax windfall.
oil: Under oil windfall profits, Russia 's GDP should have grown by 15 % to 16 % in 2005.