The answer on this question can be found in article 2 of the standard Interhouse tenancy agreement and article 3 of the Interhouse letting agents Amsterdam VVA tenancy agreement.
The tenancy agreement must be terminated by means of a signed letter of notice. You can find a template here. You need to take the agreed period of notice into account. Termination is only possible per the end of the month (i.e. not as of 14 March, for example, but as of 31 March). If the tenant terminates the agreement and more than one tenant is named on the agreement, each individual tenant must sign the letter of notice. According to the tenancy agreement, the letter of notice must be sent by bailiff’s notification or registered post. Are you a tenant? Check with your landlord/manager whether sending the signed termination letter per e-mail (with confirmation of receipt) is also sufficient.