Again. If it's a US company it stops right there- the FBI can get what it wants, this 'foreign account' or Irish server issue doesn't matter. The FBI won't need permission, it won't disclose anything about the investigation with a foreign government- it doesn't have to. They might alert the foreign government when it comes time to arrest someone- then of course the FBI might work with a foreign government to locate their target. But in the phase of gathering information and surveillance on a target, that's not necessarily going to happen in a sensitive or confidential national security matter.
The reverse is not true, however- non US authorities would have to go through hoops to get data on a US based account.
18 USC 2703 does not make a distinction about the origin of the records- it just says a service provider is compelled with appropriate legal process. In fact a Homeland Security agency gathers records because they are foreign. Even local police agencies get that information. Example- someone in Chicago is a victim of a Nigerian scam using a US based email service, the crime originates in Nigeria (although they don't know that yet). The victim goes to their local police department in Chicago, which has a high technology crimes unit. They issue an investigative subpoena for subscriber information to find out who they're dealing with, they discover at that point when the get the records from the company pursuant to a subpoena by tracing the IP address that it leads back to Nigeria, and say to the victim, "ok, we can't do anything more than that, the scam is out of our jurisdiction, and we don't have any connections with the Nigerian government."
Or, let's say it were something to do with FISA or national security. Once, again, the FBI investigates a foreign account, they go and get a warrant and search the mail account contents. It makes no difference if the target is from Yemen or Pakistan or the UK- in all cases, this is a US company, it falls under US laws, or do people think the FBI gets permission from the Pakistani government to do that? At the same time, a US agency has to comply with US privacy laws and the US Constitution, whether investigating a US or foreign target. So even a foreign account still has protection from illegal search and seizure under US law. But there's no more to it than this. If people deny this is the way it works, there's not much more than I can say other than to suggest they don't have to worry about anything, since evidently US government agencies can't get that information according to their beliefs (yet at the same time, they seem to be criticizing the fact that the US is getting this information somehow, which is a contradiction to their belief that the US can't get this information).
We've all heard of the Patriot Act, right? The PA would be completely nullified if it mattered that these were foreign accounts, that's the whole point of the Patriot Act- to gather information on foreign accounts. But it doesn't stop with the Patriot Act. A government agency, say even a local police department isn't necessarily constrained, they can get information under their own local laws, and under 18 USC 2703. The reason why is that it is a US based company- location of servers won't matter except to tack on additional enhancements to a crime, such as when illegal activity crosses multiple jurisdictions.
No one gets out of here alive.