Yes, they are still valid for postage in the US. Your total value must still meet the proper amount. Currently in the US that is 44 cents for mail.
As postage to mail something like a letter.
No of course not! you'd need an airmail stamp.
That is what you do with a stamp, put it on a letter to pay for it to be delivered. You always use the postage from the country you are mailing the item in.
The stamp has to be accepted where you mail the letter. If you are mailing in Canada, you need a Canadian stamp. If you are in the US mailing to Canada, you can use a US stamp.
The value of the Forever Stamp is the domestic First-Class Mail letter price in effect on the day of use.
To mail a single letter to Canada, the stamp must be equivalent to the postage cost. As long as the stamp is equal to the postage, any letter can be sent with any kind of postage stamp.
To send a letter to the UK, First Class (that's Air Mail,) the stamp costs $1.02.
No, you can only use British stamps for mail posted in London. (You wouldn't expect to be able to use a stamp from a different country on a letter mailed in the USA.)
Type your answer here... Can I use a 55 cent Alice Hamilton stamp to mail a letter todayi?
a letter weighing 1 gram to Eire, what postage do I need?
If you are posting it in the US, yes. As long as the amount on the stamp covers the overseas postal charge.
No, you cannot. You must meet the cost for a letter which will be 98 cents. The Forever stamp is only 44 cents.