Service of documents
Service is complicated. Effecting valid service depends on what is being sent, by whom, to whom, how, where and when. There are cases of all sizes that turn on when and if a person was validly served with a document and the laws vary widely by jurisdiction and, within a jurisdiction, with what is being served and whether the person being served is a natural person or a body corporate.
I can't help you for israel.
However, in australia, the Commonwealth and sech State and territory have an Electronic Transactions Act which spells this out (although other laws may not allow electronic service, for example, of court papers).
Since contract/employment law is a state matter in Australia, I will quote s13A of the new-south-wales law (noting that other Australian jurisdictions are similar):
13A TIME OF RECEIPT
(1) For the purposes of a law of this jurisdiction, unless otherwise agreed between the originator and the addressee of an electronic communication--
(a) the time of receipt of the electronic communication is the time when the electronic communication becomes capable of being retrieved by the addressee at an electronic address designated by the addressee, or
(b) the time of receipt of the electronic communication at another electronic address of the addressee is the time when both--
(i) the electronic communication has become capable of being retrieved by the addressee at that address, and
(ii) the addressee has become aware that the electronic communication has been sent to that address.
(2) For the purposes of subsection (1), unless otherwise agreed between the originator and the addressee of the electronic communication, it is to be assumed that the electronic communication is capable of being retrieved by the addressee when it reaches the addressee's electronic address.
So, if your person (let's call her Jane), had designated that email address to the company as a point of contact, then, unless they had agreed otherwise, Jane would have received it when it hit her Spam folder. If so, the company (probably1) has no liability to pay for the 4 or 5 extra hours worked.
However, if she had not designated the address, then she would have received it when the company told her about it. If so, the company would owe her for the hours worked.
So, if this was an address that Jane had provided to the company or one that Jane had agreed could be used to communicate with her, too bad for Jane. However, if the company had found this address in a LinkedIn profile and Jane had not "designated" it, too bad for the company.
Now, this is a small matter of a few hours. However, let's imagine this was an order to suspend work on a major contract with 1,000 people working for 40 hours per week for 4 weeks ant an average cost of $120 (about $5,000,000). Or imagine it's an attempt to lodge an appeal against deportation. You can see why these things go to court.
1Ignoring an equitable claim for unjust enrichment and assuming that the reduction in hours did not require Jane's consent under the contract.