Alternatively, you can always find an email server you trust to relay through. That'll help, but, you risk the relay monitoring your email. Email is inherently insecure, so relying upon it for secrecy is a fools errand anyways.
I realize that the last email was really about a question related to spam filters, rather than about email security. So sorry in advance for the bikeshedding. Still, since the idea that "[e]mail is inherently insecure" is so widespread, I want to take this opportunity to voice my disagreement. So here are two reasons for why I think that email is actually a lot better than its reputation: First, TLS adoption is pretty comprehensive in the modern email ecosystem. And second, end-to-end-encrypted email can be both reasonably secure and easy to use; at least if you use the right app for it.
To elaborate on the first reason: TLS adoption. Delivering an email takes three hops: hop 1 from Alice to Provider A, hop 2 from Provider A to Provider B, and hop 3 from Provider B to Bob. All providers I know of have been offering SMTPS for hop 1 and IMAPS for hop 3 for well over a decade now. I am not even sure how many providers still offer support for the non-TLS-variants of those two protocols. And even if providers offer both TLS-enabled and non-TLS variants of those protocols, all reasonably configured user agents should use the TLS-enabled version anyhow. Which then leaves us with hop 2 between Provider A and Provider B. When TLS encryption was only just starting to appear, email providers would often fall back on plain SMTP for hop 2 if one of them did not support TLS yet. However, I do not think that this is the case any more; and for a good reason: My own email provider (posteo.de) offers a setting to enforce TLS for hop 2. If I enable this setting for outgoing email, and posteo cannot deliver the message via SMTPS, instead of trying to fall back on non-TLS SMTP, it will inform me that delivery of the message has failed. Likewise, if I enable this setting for incoming email, and some provider tries to deliver an email via non-TLS SMTP, posteo will reject that message and inform both the sender and myself that delivery has failed. I enabled both settings a couple of years ago. And how many deliveries have failed due to missing TLS support? Zero. Not a single one. This means that in the last couple of years, not a single being has tried to get an email to me without using TLS for hop 2. Not even the spammers (and I have actually received quite a bit of spam).
To conclude the first reason: Email takes three hops to be delivered; and all three hops are protected via TLS. Therefore, the same security guarantees that make HTTPS "secure" (TM) ensure that only four parties can read an email from Alice to Bob. That is: Alice, Provider A, Provider B, and Bob. On the one hand, this might not seem like a particularly strong guarantee of confidentiality, since it assumes that both Alice and Bob trust their providers. However, exactly this caveat of having to trust the provider is commonly accepted in our computing environments without being labelled as "inherently insecure". If Some User decides to use Some Big Cloud Provider to sync data between their devices -- or as a backup solution --, this is commonly accepted without anyone calling it "inherently insecure." If some Random Company hosts their online shop on some VPS in some Third Party Data Centre, this is also commonly viewed as being entirely acceptable. So yes, standard TLS-encrypted email can only be called "secure" as long as users trust their email providers. But no, this does not make email "inherently insecure." It just means that the security guarantees the system provides are comparable to what you get with using HTTPS to connect to virtual machines hosted in data centres -- which, in most contexts, would be regarded as the epitome of security (TM).
To elaborate on the second reason: I realize that OpenPGP has been the target of a good amount of criticism. And I will in no way try to argue that this criticism has been ill-informed. Indeed, I believe that a lot of this criticism has been quite to the point. Both the criticism focussed on the cryptographic setup and especially the criticism focussed on the UI/UX part. However, since the standards surrounding OpenPGP-encrypted email are so comprehensive, they also include a number of things that are not entirely bad. Delta Chat (https://delta.chat/), for instance, is an email client that uses a very small subset of OpenPGP-encrypted email to implement pretty reasonable end-to-end encryption. If you are interested in what modern end-to-end-encrypted email can look like, you might really want to check out what they are doing. Some of the highlights include: using cv25519/ed25519 (only) for encryption and signatures, using QR-Codes to exchange fingerprints, and spoofing envelope headers to protect message metadata and even to implement masked sending for end-to-end-encrypted email. And all that with a UI that is at least as beginner-friendly as Whatsapp's. So if both Alice and Bob agree to use Delta Chat for their communication, they do not even need to trust Provider A and Provider B any more. This is not to say that Delta Chat is infallible; and their decision to stay at least one-way compatible with existing implementations of OpenPGP does imply certain ramifications in other areas, such as future secrecy or post quantum security. So depending on which kind of attacker you are trying to guard against, Delta Chat might not be what you are looking for. Still, I would certainly argue that the security guarantees Delta Chat provides for end-to-end-encrypted email are way too good for it to be labelled an "inherently insecure" cryptographic system. Particularly so if we call systems like SSH or HTTPS "secure" at the same time.
So, this is my quick rant about the myth that email is "inherently insecure". I am not saying that email is perfect. I am not saying that the mechanisms mentioned above solve all cryptographic problems. But if I am lucky, I might have managed to make some of you question the myth that every email is essentially a world-readable post-card. Email might not be the most secure system there is; but it is still a lot better than what most people seem to assume.
Best
Frank