All investors are unique. But one common theme of the most successful investment portfolios is their tendency to lean on dividend stocks.

This shouldn't surprise anyone. Companies that pay a dividend are almost always profitable, have time-tested operating models, and usually have excellent visibility into the future. It also doesn't hurt that dividend stocks have absolutely run circles around their non-dividend-paying peers over the long run.

But income seekers face a dilemma. They want the highest yield possible with the least amount of risk. The data shows that once a payout hits high-yield status (4% or higher), realized returns can get dicey. In other words, high-yield dividend stocks can sometimes be more trouble than they're worth.

However, that's not the case with the following five high-yield dividend payers. These are, in my view, five of the safest high-yield dividend stocks on the planet.

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Verizon Communications: 4.4% yield

With the exception of utility stocks, there's probably not an industry or niche that generates more consistent cash flow or pays persistently high dividends than telecommunications. Even though AT&T boasts the higher yield, the safest telecom payout of all goes to Verizon (NYSE:VZ) at 4.4%.

As noted, predictability plays a key role in Verizon's success. It's been a good decade since wireless download speeds improved in this country. The rollout of 5G infrastructure offers consumers and businesses the motivation they need to upgrade their devices and download more data. Since Verizon's wireless segment benefits from high-margin data consumption, the 5G revolution is a pathway to sustainable low- to mid-single-digit organic wireless growth.

Beyond its wireless operations, Verizon is spreading its wings into broadband services. The company has spared no expense to purchase 5G mid-band spectrum. The expectation is that this will help Verizon reach 30 million homes with its broadband services by the end of 2023.

With a payout ratio right around 50%, high-yield dividend stocks don't get much safer than Verizon.

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Enterprise Products Partners: 7.3% yield

You probably wouldn't think of companies in the oil and gas industry as "safe," especially considering the pummeling that crude oil took in the wake of the coronavirus pandemic last year. But master-limited partnership Enterprise Products Partners (NYSE:EPD) stands out as an exception to the rule.

Enterprise Products Partners is a midstream energy company. Instead of drilling for oil and natural gas (upstream) or refining petroleum products (downstream), it predominantly handles the transmission and storage of oil, natural gas, and natural gas liquids. It has over 50,000 miles of pipeline and roughly 14 billion cubic feet of natural gas storage capacity, most of which is located in the Midwest and southern U.S. states.

Midstream companies like Enterprise Products Partners generate highly predictable cash flow with long-term fee-based contracts. It regularly outlays capital to invest in new pipeline and storage projects and isn't afraid to make acquisitions to adjust to a landscape that will eventually lean toward cleaner energy solutions.

Most important, Enterprise Products Partners' distribution coverage ratio -- a measure of distributable cash flow divided by distributions to be paid -- never came close to dropping below 1 in 2020. In fact, it's consistently been in the high 1s, signifying a rock-solid and sustainable payout.

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Philip Morris International: 5% yield

Another exceptionally safe high-yield stock income seekers can count on is tobacco giant Philip Morris International (NYSE:PM). The company is behind the well-known premium tobacco brand Marlboro.

To state the obvious, the nicotine found in tobacco is an addictive chemical. This means cigarette smokers tend to remain users for long periods of time. Even with health regulators loudly raising concerns about the dangers of smoking, Philip Morris has been able to use its strong pricing power to outweigh volume declines in developed markets.

Philip Morris also benefits from its geographic diversity. It doesn't operate in the U.S. but has operations in more than 180 other countries worldwide. This means it can offset tighter tobacco regulations in certain developed markets with growth from burgeoning middle classes in select emerging markets.

With Philip Morris paying out a hearty but still sustainable 72% of Wall Street's forecasted earnings per share in 2022, it's clear that rewarding patient shareholders is a priority.

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AGNC Investment Corp.: 7.7% yield

Few industries have been more universally disliked by Wall Street over the past decade than mortgage real estate investment trusts (REITs). But in spite of Wall Street's distaste, mortgage REIT AGNC Investment Corp. (NASDAQ:AGNC) has consistently delivered a high-single-digit or low-double-digit yield. This should be the expectation for income seekers going forward.

Mortgage REITs like AGNC seek to borrow money at low short-term borrowing rates to purchase assets, such as mortgage-backed securities, with higher long-term yields. The difference between this higher long-term yield and lower short-term borrowing rate is known as the net interest margin (NIM). What's worth noting is that the yield curve traditionally steepens during the early stages of an economic recovery. For mortgage REITs like AGNC, it means we've hit the sweet spot of their growth cycle where NIM widens.

The other factor to consider is that AGNC Investment has completely revamped its asset portfolio to focus almost exclusively on agency securities. An agency security is protected by the federal government in the event of a default. Although the yield on agency assets is lower than their non-agency counterparts, this added protection allows AGNC to use leverage to its advantage.

As one final note, AGNC Investment parses out its rock-solid dividend on a monthly basis.

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IBM: 4.4% yield

Tech stocks certainly aren't known for their high yields, but that's exactly what you're going to get with tech stalwart IBM (NYSE:IBM). Its 4.4% payout can handily outpace the prevailing inflation rate, and it's easily one of the world's safest high-yield dividend stocks.

Even though IBM's stock hasn't been a top-performer over the past decade, the company continues to generate boatloads of profit and cash flow as a result of two factors. First, IBM has gone all-in on its hybrid-cloud solutions and artificial intelligence. It paid the price for its late entrance to cloud computing but has used innovation and acquisitions to claw its way back. As of the first quarter of 2021, about 37% of its total revenue derived from high-margin cloud services.

The other important factor here is IBM's measured cost-cutting for its legacy operations. Though its legacy software sales are typically flat or in slight decline, being mindful of expenses has kept its margins up. As a result, the cash flow IBM is generating from these legacy operations is helping to reduce its debt and fund its juicy dividend.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.